No live SolrServers available to handle this request

Haber001 2015-08-20 11:39:50

solr vesion: 5.2.1
zookeeper version: 3.4.6

do load test:
2 instances solr, 3 instances zookeeper.
100 thread requests(50 no errors).

org.apache.solr.client.solrj.SolrServerException: No live SolrServers available to handle this request
at org.apache.solr.client.solrj.impl.LBHttpSolrClient.request(LBHttpSolrClient.java:570)
at org.apache.solr.client.solrj.SolrRequest.process(SolrRequest.java:135)
at org.apache.solr.client.solrj.SolrClient.query(SolrClient.java:975)
at org.apache.solr.client.solrj.SolrClient.query(SolrClient.java:991)
at com.xx.xx.search.solrcloud.query.service.se.solr.SolrCloudClient.search(SolrCloudClient.java:62)
at com.xx.xx.search.solrcloud.query.SolrMultiQueryProcess$Consumer.query(SolrMultiQueryProcess.java:115)
at com.xx.xx.search.solrcloud.query.SolrMultiQueryProcess$Consumer.run(SolrMultiQueryProcess.java:96)
at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.solr.client.solrj.SolrServerException: IOException occured when talking to server at: http://xxxx:8080/solr/xxxx
at org.apache.solr.client.solrj.impl.HttpSolrClient.executeMethod(HttpSolrClient.java:570)
at org.apache.solr.client.solrj.impl.HttpSolrClient.request(HttpSolrClient.java:233)
at org.apache.solr.client.solrj.impl.HttpSolrClient.request(HttpSolrClient.java:225)
at org.apache.solr.client.solrj.impl.LBHttpSolrClient.request(LBHttpSolrClient.java:520)
... 7 more
Caused by: org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection from pool
at org.apache.http.impl.conn.PoolingClientConnectionManager.leaseConnection(PoolingClientConnectionManager.java:226)
at org.apache.http.impl.conn.PoolingClientConnectionManager$1.getConnection(PoolingClientConnectionManager.java:195)
at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:422)
at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:863)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:106)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:57)
at org.apache.solr.client.solrj.impl.HttpSolrClient.executeMethod(HttpSolrClient.java:462)
... 10 more

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https://issues.apache.org/jira/browse/SOLR-7951

Contents Module Overview 1 Lesson 1: Memory 3 Lesson 2: I/O 73 Lesson 3: CPU 111 Module 3: Troubleshooting Server Performance Module Overview Troubleshooting server performance-based support calls requires product knowledge, good communication skills, and a proven troubleshooting methodology. In this module we will discuss Microsoft® SQL Server™ interaction with the operating system and methodology of troubleshooting server-based problems. At the end of this module, you will be able to:  Define the common terms associated the memory, I/O, and CPU subsystems.  Describe how SQL Server leverages the Microsoft Windows® operating system facilities including memory, I/O, and threading.  Define common SQL Server memory, I/O, and processor terms.  Generate a hypothesis based on performance counters captured by System Monitor.  For each hypothesis generated, identify at least two other non-System Monitor pieces of information that would help to confirm or reject your hypothesis.  Identify at least five counters for each subsystem that are key to understanding the performance of that subsystem.  Identify three common myths associated with the memory, I/O, or CPU subsystems. Lesson 1: Memory What You Will Learn After completing this lesson, you will be able to:  Define common terms used when describing memory.  Give examples of each memory concept and how it applies to SQL Server.  Describe how SQL Server user and manages its memory.  List the primary configuration options that affect memory.  Describe how configuration options affect memory usage.  Describe the effect on the I/O subsystem when memory runs low.  List at least two memory myths and why they are not true. Recommended Reading  SQL Server 7.0 Performance Tuning Technical Reference, Microsoft Press  Windows 2000 Resource Kit companion CD-ROM documentation. Chapter 15: Overview of Performance Monitoring  Inside Microsoft Windows 2000, Third Edition, David A. Solomon and Mark E. Russinovich  Windows 2000 Server Operations Guide, Storage, File Systems, and Printing; Chapters: Evaluating Memory and Cache Usage  Advanced Windows, 4th Edition, Jeffrey Richter, Microsoft Press Related Web Sites  http://ntperformance/ Memory Definitions Memory Definitions Before we look at how SQL Server uses and manages its memory, we need to ensure a full understanding of the more common memory related terms. The following definitions will help you understand how SQL Server interacts with the operating system when allocating and using memory. Virtual Address Space A set of memory addresses that are mapped to physical memory addresses by the system. In a 32-bit operation system, there is normally a linear array of 2^32 addresses representing 4,294,967,269 byte addresses. Physical Memory A series of physical locations, with unique addresses, that can be used to store instructions or data. AWE – Address Windowing Extensions A 32-bit process is normally limited to addressing 2 gigabytes (GB) of memory, or 3 GB if the system was booted using the /3G boot switch even if there is more physical memory available. By leveraging the Address Windowing Extensions API, an application can create a fixed-size window into the additional physical memory. This allows a process to access any portion of the physical memory by mapping it into the applications window. When used in combination with Intel’s Physical Addressing Extensions (PAE) on Windows 2000, an AWE enabled application can support up to 64 GB of memory Reserved Memory Pages in a processes address space are free, reserved or committed. Reserving memory address space is a way to reserve a range of virtual addresses for later use. If you attempt to access a reserved address that has not yet been committed (backed by memory or disk) you will cause an access violation. Committed Memory Committed pages are those pages that when accessed in the end translate to pages in memory. Those pages may however have to be faulted in from a page file or memory mapped file. Backing Store Backing store is the physical representation of a memory address. Page Fault (Soft/Hard) A reference to an invalid page (a page that is not in your working set) is referred to as a page fault. Assuming the page reference does not result in an access violation, a page fault can be either hard or soft. A hard page fault results in a read from disk, either a page file or memory-mapped file. A soft page fault is resolved from one of the modified, standby, free or zero page transition lists. Paging is represented by a number of counters including page faults/sec, page input/sec and page output/sec. Page faults/sec include soft and hard page faults where as the page input/output counters represent hard page faults. Unfortunately, all of these counters include file system cache activity. For more information, see also…Inside Windows 2000,Third Edition, pp. 443-451. Private Bytes Private non-shared committed address space Working Set The subset of processes virtual pages that is resident in physical memory. For more information, see also… Inside Windows 2000,Third Edition, p. 455. System Working Set Like a process, the system has a working set. Five different types of pages represent the system’s working set: system cache; paged pool; pageable code and data in the kernel; page-able code and data in device drivers; and system mapped views. The system working set is represented by the counter Memory: cache bytes. System working set paging activity can be viewed by monitoring the Memory: Cache Faults/sec counter. For more information, see also… Inside Windows 2000,Third Edition, p. 463. System Cache The Windows 2000 cache manager provides data caching for both local and network file system drivers. By caching virtual blocks, the cache manager can reduce disk I/O and provide intelligent read ahead. Represented by Memory:Cache Resident bytes. For more information, see also… Inside Windows 2000,Third Edition, pp. 654-659. Non Paged Pool Range of addresses guaranteed to be resident in physical memory. As such, non-paged pool can be accessed at any time without incurring a page fault. Because device drivers operate at DPC/dispatch level (covered in lesson 2), and page faults are not allowed at this level or above, most device drivers use non-paged pool to assure that they do not incur a page fault. Represented by Memory: Pool Nonpaged Bytes, typically between 3-30 megabytes (MB) in size. Note The pool is, in effect, a common area of memory shared by all processes. One of the most common uses of non-paged pool is the storage of object handles. For more information regarding “maximums,” see also… Inside Windows 2000,Third Edition, pp. 403-404 Paged Pool Range of address that can be paged in and out of physical memory. Typically used by drivers who need memory but do not need to access that memory from DPC/dispatch of above interrupt level. Represented by Memory: Pool Paged Bytes and Memory:Pool Paged Resident Bytes. Typically between 10-30MB + size of Registry. For more information regarding “limits,” see also… Inside Windows 2000,Third Edition, pp. 403-404. Stack Each thread has two stacks, one for kernel mode and one for user mode. A stack is an area of memory in which program procedure or function call addresses and parameters are temporarily stored. In Process To run in the same address space. In-process servers are loaded in the client’s address space because they are implemented as DLLs. The main advantage of running in-process is that the system usually does not need to perform a context switch. The disadvantage to running in-process is that DLL has access to the process address space and can potentially cause problems. Out of Process To run outside the calling processes address space. OLEDB providers can run in-process or out of process. When running out of process, they run under the context of DLLHOST.EXE. Memory Leak To reserve or commit memory and unintentionally not release it when it is no longer being used. A process can leak resources such as process memory, pool memory, user and GDI objects, handles, threads, and so on. Memory Concepts (X86 Address Space) Per Process Address Space Every process has its own private virtual address space. For 32-bit processes, that address space is 4 GB, based on a 32-bit pointer. Each process’s virtual address space is split into user and system partitions based on the underlying operating system. The diagram included at the top represents the address partitioning for the 32-bit version of Windows 2000. Typically, the process address space is evenly divided into two 2-GB regions. Each process has access to 2 GB of the 4 GB address space. The upper 2 GB of address space is reserved for the system. The user address space is where application code, global variables, per-thread stacks, and DLL code would reside. The system address space is where the kernel, executive, HAL, boot drivers, page tables, pool, and system cache reside. For specific information regarding address space layout, refer to Inside Microsoft Windows 2000 Third Edition pages 417-428 by Microsoft Press. Access Modes Each virtual memory address is tagged as to what access mode the processor must be running in. System space can only be accessed while in kernel mode, while user space is accessible in user mode. This protects system space from being tampered with by user mode code. Shared System Space Although every process has its own private memory space, kernel mode code and drivers share system space. Windows 2000 does not provide any protection to private memory being use by components running in kernel mode. As such, it is very important to ensure components running in kernel mode are thoroughly tested. 3-GB Address Space 3-GB Address Space Although 2 GB of address space may seem like a large amount of memory, application such as SQL Server could leverage more memory if it were available. The boot.ini option /3GB was created for those cases where systems actually support greater than 2 GB of physical memory and an application can make use of it This capability allows memory intensive applications running on Windows 2000 Advanced Server to use up to 50 percent more virtual memory on Intel-based computers. Application memory tuning provides more of the computer's virtual memory to applications by providing less virtual memory to the operating system. Although a system having less than 2 GB of physical memory can be booted using the /3G switch, in most cases this is ill-advised. If you restart with the 3 GB switch, also known as 4-Gig Tuning, the amount of non-paged pool is reduced to 128 MB from 256 MB. For a process to access 3 GB of address space, the executable image must have been linked with the /LARGEADDRESSAWARE flag or modified using Imagecfg.exe. It should be pointed out that SQL Server was linked using the /LAREGEADDRESSAWARE flag and can leverage 3 GB when enabled. Note Even though you can boot Windows 2000 Professional or Windows 2000 Server with the /3GB boot option, users processes are still limited to 2 GB of address space even if the IMAGE_FILE_LARGE_ADDRESS_AWARE flag is set in the image. The only thing accomplished by using the /3G option on these system is the reduction in the amount of address space available to the system (ISW2K Pg. 418). Important If you use /3GB in conjunction with AWE/PAE you are limited to 16 GB of memory. For more information, see the following Knowledge Base articles: Q171793 Information on Application Use of 4GT RAM Tuning Q126402 PagedPoolSize and NonPagedPoolSize Values in Windows NT Q247904 How to Configure Paged Pool and System PTE Memory Areas Q274598 W2K Does Not Enable Complete Memory Dumps Between 2 & 4 GB AWE Memory Layout AWE Memory Usually, the operation system is limited to 4 GB of physical memory. However, by leveraging PAE, Windows 2000 Advanced Server can support up to 8 GB of memory, and Data Center 64 GB of memory. However, as stated previously, each 32-bit process normally has access to only 2 GB of address space, or 3 GB if the system was booted with the /3-GB option. To allow processes to allocate more physical memory than can be represented in the 2GB of address space, Microsoft created the Address Windows Extensions (AWE). These extensions allow for the allocation and use of up to the amount of physical memory supported by the operating system. By leveraging the Address Windowing Extensions API, an application can create a fixed-size window into the physical memory. This allows a process to access any portion of the physical memory by mapping regions of physical memory in and out of the applications window. The allocation and use of AWE memory is accomplished by  Creating a window via VirtualAlloc using the MEM_PHYSICAL option  Allocating the physical pages through AllocateUserPhysicalPages  Mapping the RAM pages to the window using MapUserPhysicalPages Note SQL Server 7.0 supports a feature called extended memory in Windows NT® 4 Enterprise Edition by using a PSE36 driver. Currently there are no PSE drivers for Windows 2000. The preferred method of accessing extended memory is via the Physical Addressing Extensions using AWE. The AWE mapping feature is much more efficient than the older process of coping buffers from extended memory into the process address space. Unfortunately, SQL Server 7.0 cannot leverage PAE/AWE. Because there are currently no PSE36 drivers for Windows 2000 this means SQL Server 7.0 cannot support more than 3GB of memory on Windows 2000. Refer to KB article Q278466. AWE restrictions  The process must have Lock Pages In Memory user rights to use AWE Important It is important that you use Enterprise Manager or DMO to change the service account. Enterprise Manager and DMO will grant all of the privileges and Registry and file permissions needed for SQL Server. The Service Control Panel does NOT grant all the rights or permissions needed to run SQL Server.  Pages are not shareable or page-able  Page protection is limited to read/write  The same physical page cannot be mapped into two separate AWE regions, even within the same process.  The use of AWE/PAE in conjunction with /3GB will limit the maximum amount of supported memory to between 12-16 GB of memory.  Task manager does not show the correct amount of memory allocated to AWE-enabled applications. You must use Memory Manager: Total Server Memory. It should, however, be noted that this only shows memory in use by the buffer pool.  Machines that have PAE enabled will not dump user mode memory. If an event occurs in User Mode Memory that causes a blue screen and root cause determination is absolutely necessary, the machine must be booted with the /NOPAE switch, and with /MAXMEM set to a number appropriate for transferring dump files.  With AWE enabled, SQL Server will, by default, allocate almost all memory during startup, leaving 256 MB or less free. This memory is locked and cannot be paged out. Consuming all available memory may prevent other applications or SQL Server instances from starting. Note PAE is not required to leverage AWE. However, if you have more than 4GB of physical memory you will not be able to access it unless you enable PAE. Caution It is highly recommended that you use the “max server memory” option in combination with “awe enabled” to ensure some memory headroom exists for other applications or instances of SQL Server, because AWE memory cannot be shared or paged. For more information, see the following Knowledge Base articles: Q268363 Intel Physical Addressing Extensions (PAE) in Windows 2000 Q241046 Cannot Create a dump File on Computers with over 4 GB RAM Q255600 Windows 2000 utilities do not display physical memory above 4GB Q274750 How to configure SQL Server memory more than 2 GB (Idea) Q266251 Memory dump stalls when PAE option is enabled (Idea) Tip The KB will return more hits if you query on PAE rather than AWE. Virtual Address Space Mapping Virtual Address Space Mapping By default Windows 2000 (on an X86 platform) uses a two-level (three-level when PAE is enabled) page table structure to translate virtual addresses to physical addresses. Each 32-bit address has three components, as shown below. When a process accesses a virtual address the system must first locate the Page Directory for the current process via register CR3 (X86). The first 10 bits of the virtual address act as an index into the Page Directory. The Page Directory Entry then points to the Page Frame Number (PFN) of the appropriate Page Table. The next 10 bits of the virtual address act as an index into the Page Table to locate the appropriate page. If the page is valid, the PTE contains the PFN of the actual page in memory. If the page is not valid, the memory management fault handler locates the page and attempts to make it valid. The final 12 bits act as a byte offset into the page. Note This multi-step process is expensive. This is why systems have translation look aside buffers (TLB) to speed up the process. One of the reasons context switching is so expensive is the translation buffers must be dumped. Thus, the first few lookups are very expensive. Refer to ISW2K pages 439-440. Core System Memory Related Counters Core System Memory Related Counters When evaluating memory performance you are looking at a wide variety of counters. The counters listed here are a few of the core counters that give you quick overall view of the state of memory. The two key counters are Available Bytes and Committed Bytes. If Committed Bytes exceeds the amount of physical memory in the system, you can be assured that there is some level of hard page fault activity happening. The goal of a well-tuned system is to have as little hard paging as possible. If Available Bytes is below 5 MB, you should investigate why. If Available Bytes is below 4 MB, the Working Set Manager will start to aggressively trim the working sets of process including the system cache.  Committed Bytes Total memory, including physical and page file currently committed  Commit Limit • Physical memory + page file size • Represents the total amount of memory that can be committed without expanding the page file. (Assuming page file is allowed to grow)  Available Bytes Total physical memory currently available Note Available Bytes is a key indicator of the amount of memory pressure. Windows 2000 will attempt to keep this above approximately 4 MB by aggressively trimming the working sets including system cache. If this value is constantly between 3-4 MB, it is cause for investigation. One counter you might expect would be for total physical memory. Unfortunately, there is no specific counter for total physical memory. There are however many other ways to determine total physical memory. One of the most common is by viewing the Performance tab of Task Manager. Page File Usage The only counters that show current page file space usage are Page File:% Usage and Page File:% Peak Usage. These two counters will give you an indication of the amount of space currently used in the page file. Memory Performance Memory Counters There are a number of counters that you need to investigate when evaluating memory performance. As stated previously, no single counter provides the entire picture. You will need to consider many different counters to begin to understand the true state of memory. Note The counters listed are a subset of the counters you should capture. *Available Bytes In general, it is desirable to see Available Bytes above 5 MB. SQL Servers goal on Intel platforms, running Windows NT, is to assure there is approximately 5+ MB of free memory. After Available Bytes reaches 4 MB, the Working Set Manager will start to aggressively trim the working sets of process and, finally, the system cache. This is not to say that working set trimming does not happen before 4 MB, but it does become more pronounced as the number of available bytes decreases below 4 MB. Page Faults/sec Page Faults/sec represents the total number of hard and soft page faults. This value includes the System Working Set as well. Keep this in mind when evaluating the amount of paging activity in the system. Because this counter includes paging associated with the System Cache, a server acting as a file server may have a much higher value than a dedicated SQL Server may have. The System Working Set is covered in depth on the next slide. Because Page Faults/sec includes soft faults, this counter is not as useful as Pages/sec, which represents hard page faults. Because of the associated I/O, hard page faults tend to be much more expensive. *Pages/sec Pages/sec represent the number of pages written/read from disk because of hard page faults. It is the sum of Memory: Pages Input/sec and Memory: Pages Output/sec. Because it is counted in numbers of pages, it can be compared to other counts of pages, such as Memory: Page Faults/sec, without conversion. On a well-tuned system, this value should be consistently low. In and of itself, a high value for this counter does not necessarily indicate a problem. You will need to isolate the paging activity to determine if it is associated with in-paging, out-paging, memory mapped file activity or system cache. Any one of these activities will contribute to this counter. Note Paging in and of itself is not necessarily a bad thing. Paging is only “bad” when a critical process must wait for it’s pages to be in-paged, or when the amount of read/write paging is causing excessive kernel time or disk I/O, thus interfering with normal user mode processing. Tip (Memory: Pages/sec) / (PhysicalDisk: Disk Bytes/sec * 4096) yields the approximate percentage of paging to total disk I/O. Note, this is only relevant on X86 platforms with a 4 KB page size. Page Reads/sec (Hard Page Fault) Page Reads/sec is the number of times the disk was accessed to resolve hard page faults. It includes reads to satisfy faults in the file system cache (usually requested by applications) and in non-cached memory mapped files. This counter counts numbers of read operations, without regard to the numbers of pages retrieved by each operation. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval. Page Writes/sec (Hard Page Fault) Page Writes/sec is the number of times pages were written to disk to free up space in physical memory. Pages are written to disk only if they are changed while in physical memory, so they are likely to hold data, not code. This counter counts write operations, without regard to the number of pages written in each operation. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval. *Pages Input/sec (Hard Page Fault) Pages Input/sec is the number of pages read from disk to resolve hard page faults. It includes pages retrieved to satisfy faults in the file system cache and in non-cached memory mapped files. This counter counts numbers of pages, and can be compared to other counts of pages, such as Memory:Page Faults/sec, without conversion. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval. This is one of the key counters to monitor for potential performance complaints. Because a process must wait for a read page fault this counter, read page faults have a direct impact on the perceived performance of a process. *Pages Output/sec (Hard Page Fault) Pages Output/sec is the number of pages written to disk to free up space in physical memory. Pages are written back to disk only if they are changed in physical memory, so they are likely to hold data, not code. A high rate of pages output might indicate a memory shortage. Windows NT writes more pages back to disk to free up space when physical memory is in short supply. This counter counts numbers of pages, and can be compared to other counts of pages, without conversion. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval. Like Pages Input/sec, this is one of the key counters to monitor. Processes will generally not notice write page faults unless the disk I/O begins to interfere with normal data operations. Demand Zero Faults/Sec (Soft Page Fault) Demand Zero Faults/sec is the number of page faults that require a zeroed page to satisfy the fault. Zeroed pages, pages emptied of previously stored data and filled with zeros, are a security feature of Windows NT. Windows NT maintains a list of zeroed pages to accelerate this process. This counter counts numbers of faults, without regard to the numbers of pages retrieved to satisfy the fault. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval. Transition Faults/Sec (Soft Page Fault) Transition Faults/sec is the number of page faults resolved by recovering pages that were on the modified page list, on the standby list, or being written to disk at the time of the page fault. The pages were recovered without additional disk activity. Transition faults are counted in numbers of faults, without regard for the number of pages faulted in each operation. This counter displays the difference between the values observed in the last two samples, divided by the duration of the sample interval. System Working Set System Working Set Like processes, the system page-able code and data are managed by a working set. For the purpose of this course, that working set is referred to as the System Working Set. This is done to differentiate the system cache portion of the working set from the entire working set. There are five different types of pages that make up the System Working Set. They are: system cache; paged pool; page-able code and data in ntoskrnl.exe; page-able code, and data in device drivers and system-mapped views. Unfortunately, some of the counters that appear to represent the system cache actually represent the entire system working set. Where noted system cache actually represents the entire system working set. Note The counters listed are a subset of the counters you should capture. *Memory: Cache Bytes (Represents Total System Working Set) Represents the total size of the System Working Set including: system cache; paged pool; pageable code and data in ntoskrnl.exe; pageable code and data in device drivers; and system-mapped views. Cache Bytes is the sum of the following counters: System Cache Resident Bytes, System Driver Resident Bytes, System Code Resident Bytes, and Pool Paged Resident Bytes. Memory: System Cache Resident Bytes (System Cache) System Cache Resident Bytes is the number of bytes from the file system cache that are resident in physical memory. Windows 2000 Cache Manager works with the memory manager to provide virtual block stream and file data caching. For more information, see also…Inside Windows 2000,Third Edition, pp. 645-650 and p. 656. Memory: Pool Paged Resident Bytes Represents the physical memory consumed by Paged Pool. This counter should NOT be monitored by itself. You must also monitor Memory: Paged Pool. A leak in the pool may not show up in Pool paged Resident Bytes. Memory: System Driver Resident Bytes Represents the physical memory consumed by driver code and data. System Driver Resident Bytes and System Driver Total Bytes do not include code that must remain in physical memory and cannot be written to disk. Memory: System Code Resident Bytes Represents the physical memory consumed by page-able system code. System Code Resident Bytes and System Code Total Bytes do not include code that must remain in physical memory and cannot be written to disk. Working Set Performance Counter You can measure the number of page faults in the System Working Set by monitoring the Memory: Cache Faults/sec counter. Contrary to the “Explain” shown in System Monitor, this counter measures the total amount of page faults/sec in the System Working Set, not only the System Cache. You cannot measure the performance of the System Cache using this counter alone. For more information, see also…Inside Windows 2000,Third Edition, p. 656. Note You will find that in general the working set manager will usually trim the working sets of normal processes prior to trimming the system working set. System Cache System Cache The Windows 2000 cache manager provides a write-back cache with lazy writing and intelligent read-ahead. Files are not written to disk immediately but differed until the cache manager calls the memory manager to flush the cache. This helps to reduce the total number of I/Os. Once per second, the lazy writer thread queues one-eighth of the dirty pages in the system cache to be written to disk. If this is not sufficient to meet the needs, the lazy writer will calculate a larger value. If the dirty page threshold is exceeded prior to lazy writer waking, the cache manager will wake the lazy writer. Important It should be pointed out that mapped files or files opened with FILE_FLAG_NO_BUFFERING, do not participate in the System Cache. For more information regarding mapped views, see also…Inside Windows 2000,Third Edition, p. 669. For those applications that would like to leverage system cache but cannot tolerate write delays, the cache manager supports write through operations via the FILE_FLAG_WRITE_THROUGH. On the other hand, an application can disable lazy writing by using the FILE_ATTRIBUTE_TEMPORARY. If this flag is enabled, the lazy writer will not write the pages to disk unless there is a shortage of memory or the file is closed. Important Microsoft SQL Server uses both FILE_FLAG_NO_BUFFERING and FILE_FLAG_WRITE_THROUGH Tip The file system cache is not represented by a static amount of memory. The system cache can and will grow. It is not unusual to see the system cache consume a large amount of memory. Like other working sets, it is trimmed under pressure but is generally the last thing to be trimmed. System Cache Performance Counters The counters listed are a subset of the counters you should capture. Cache: Data Flushes/sec Data Flushes/sec is the rate at which the file system cache has flushed its contents to disk as the result of a request to flush or to satisfy a write-through file write request. More than one page can be transferred on each flush operation. Cache: Data Flush Pages/sec Data Flush Pages/sec is the number of pages the file system cache has flushed to disk as a result of a request to flush or to satisfy a write-through file write request. Cache: Lazy Write Flushes/sec Represents the rate of lazy writes to flush the system cache per second. More than one page can be transferred per second. Cache: Lazy Write Pages/sec Lazy Write Pages/sec is the rate at which the Lazy Writer thread has written to disk. Note When looking at Memory:Cache Faults/sec, you can remove cache write activity by subtracting (Cache: Data Flush Pages/sec + Cache: Lazy Write Pages/sec). This will give you a better idea of how much other page faulting activity is associated with the other components of the System Working Set. However, you should note that there is no easy way to remove the page faults associated with file cache read activity. For more information, see the following Knowledge Base articles: Q145952 (NT4) Event ID 26 Appears If Large File Transfer Fails Q163401 (NT4) How to Disable Network Redirector File Caching Q181073 (SQL 6.5) DUMP May Cause Access Violation on Win2000 System Pool System Pool As documented earlier, there are two types of shared pool memory: non-paged pool and paged pool. Like private memory, pool memory is susceptible to a leak. Nonpaged Pool Miscellaneous kernel code and structures, and drivers that need working memory while at or above DPC/dispatch level use non-paged pool. The primary counter for non-paged pool is Memory: Pool Nonpaged Bytes. This counter will usually between 3 and 30 MB. Paged Pool Drivers that do not need to access memory above DPC/Dispatch level are one of the primary users of paged pool, however any process can use paged pool by leveraging the ExAllocatePool calls. Paged pool also contains the Registry and file and printing structures. The primary counters for monitoring paged pool is Memory: Pool Paged Bytes. This counter will usually be between 10-30MB plus the size of the Registry. To determine how much of paged pool is currently resident in physical memory, monitor Memory: Pool Paged Resident Bytes. Note The paged and non-paged pools are two of the components of the System Working Set. If a suspected leak is clearly visible in the overview and not associated with a process, then it is most likely a pool leak. If the leak is not associated with SQL Server handles, OLDEB providers, XPROCS or SP_OA calls then most likely this call should be pushed to the Windows NT group. For more information, see the following Knowledge Base articles: Q265028 (MS) Pool Tags Q258793 (MS) How to Find Memory Leaks by Using Pool Bitmap Analysis Q115280 (MS) Finding Windows NT Kernel Mode Memory Leaks Q177415 (MS) How to Use Poolmon to Troubleshoot Kernel Mode Memory Leaks Q126402 PagedPoolSize and NonPagedPoolSize Values in Windows NT Q247904 How to Configure Paged Pool and System PTE Memory Areas Tip To isolate pool leaks you will need to isolate all drivers and third-party processes. This should be done by disabling each service or driver one at a time and monitoring the effect. You can also monitor paged and non-paged pool through poolmon. If pool tagging has been enabled via GFLAGS, you may be able to associate the leak to a particular tag. If you suspect a particular tag, you should involve the platform support group. Process Memory Counters Process _Total Limitations Although the rollup of _Total for Process: Private Bytes, Virtual Bytes, Handles and Threads, represent the key resources being used across all processes, they can be misleading when evaluating a memory leak. This is because a leak in one process may be masked by a decrease in another process. Note The counters listed are a subset of the counters you should capture. Tip When analyzing memory leaks, it is often easier to a build either a separate chart or report showing only one or two key counters for all process. The primary counter used for leak analysis is private bytes, but processes can leak handles and threads just as easily. After a suspect process is located, build a separate chart that includes all the counters for that process. Individual Process Counters When analyzing individual process for memory leaks you should include the counters listed.  Process: % Processor Time  Process: Working Set (includes shared pages)  Process: Virtual Bytes  Process: Private Bytes  Process: Page Faults/sec  Process: Handle Count  Process: Thread Count  Process: Pool Paged Bytes  Process: Pool Nonpaged Bytes Tip WINLOGON, SVCHOST, services, or SPOOLSV are referred to as HELPER processes. They provide core functionality for many operations and as such are often extended by the addition of third-party DLLs. Tlist –s may help identify what services are running under a particular helper. Helper Processes Helper Processes Winlogon, Services, and Spoolsv and Svchost are examples of what are referred to as HELPER processes. They provide core functionality for many operations and, as such, are often extended by the addition of third-party DLLs. Running every service in its own process can waste system resources. Consequently, some services run in their own processes while others share a process with other services. One problem with sharing a process is that a bug in one service may cause the entire process to fail. The resource kit tool, Tlist when used with the –s qualifier can help you identify what services are running in what processes. WINLOGON Used to support GINAs. SPOOLSV SPOOLSV is responsible for printing. You will need to investigate all added printing functionality. Services Service is responsible for system services. Svchost.exe Svchost.exe is a generic host process name for services that are run from dynamic-link libraries (DLLs). There can be multiple instances of Svchost.exe running at the same time. Each Svchost.exe session can contain a grouping of services, so that separate services can be run depending on how and where Svchost.exe is started. This allows for better control and debugging. The Effect of Memory on Other Components Memory Drives Overall Performance Processor, cache, bus speeds, I/O, all of these resources play a roll in overall perceived performance. Without minimizing the impact of these components, it is important to point out that a shortage of memory can often have a larger perceived impact on performance than a shortage of some other resource. On the other hand, an abundance of memory can often be leveraged to mask bottlenecks. For instance, in certain environments, file system cache can significantly reduce the amount of disk I/O, potentially masking a slow I/O subsystem. Effect on I/O I/O can be driven by a number of memory considerations. Page read/faults will cause a read I/O when a page is not in memory. If the modified page list becomes too long the Modified Page Writer and Mapped Page Writer will need to start flushing pages causing disk writes. However, the one event that can have the greatest impact is running low on available memory. In this case, all of the above events will become more pronounced and have a larger impact on disk activity. Effect on CPU The most effective use of a processor from a process perspective is to spend as much time possible executing user mode code. Kernel mode represents processor time associated with doing work, directly or indirectly, on behalf of a thread. This includes items such as synchronization, scheduling, I/O, memory management, and so on. Although this work is essential, it takes processor cycles and the cost, in cycles, to transition between user and kernel mode is expensive. Because all memory management and I/O functions must be done in kernel mode, it follows that the fewer the memory resources the more cycles are going to be spent managing those resources. A direct result of low memory is that the Working Set Manager, Modified Page Writer and Mapped Page Writer will have to use more cycles attempting to free memory. Analyzing Memory Look for Trends and Trend Relationships Troubleshooting performance is about analyzing trends and trend relationships. Establishing that some event happened is not enough. You must establish the effect of the event. For example, you note that paging activity is high at the same time that SQL Server becomes slow. These two individual facts may or may not be related. If the paging is not associated with SQL Servers working set, or the disks SQL is using there may be little or no cause/affect relationship. Look at Physical Memory First The first item to look at is physical memory. You need to know how much physical and page file space the system has to work with. You should then evaluate how much available memory there is. Just because the system has free memory does not mean that there is not any memory pressure. Available Bytes in combination with Pages Input/sec and Pages Output/sec can be a good indicator as to the amount of pressure. The goal in a perfect world is to have as little hard paging activity as possible with available memory greater than 5 MB. This is not to say that paging is bad. On the contrary, paging is a very effective way to manage a limited resource. Again, we are looking for trends that we can use to establish relationships. After evaluating physical memory, you should be able to answer the following questions:  How much physical memory do I have?  What is the commit limit?  Of that physical memory, how much has the operating system committed?  Is the operating system over committing physical memory?  What was the peak commit charge?  How much available physical memory is there?  What is the trend associated with committed and available? Review System Cache and Pool Contribution After you understand the individual process memory usage, you need to evaluate the System Cache and Pool usage. These can and often represent a significant portion of physical memory. Be aware that System Cache can grow significantly on a file server. This is usually normal. One thing to consider is that the file system cache tends to be the last thing trimmed when memory becomes low. If you see abrupt decreases in System Cache Resident Bytes when Available Bytes is below 5 MB you can be assured that the system is experiencing excessive memory pressure. Paged and non-paged pool size is also important to consider. An ever-increasing pool should be an indicator for further research. Non-paged pool growth is usually a driver issue, while paged pool could be driver-related or process-related. If paged pool is steadily growing, you should investigate each process to see if there is a specific process relationship. If not you will have to use tools such as poolmon to investigate further. Review Process Memory Usage After you understand the physical memory limitations and cache and pool contribution you need to determine what components or processes are creating the pressure on memory, if any. Be careful if you opt to chart the _Total Private Byte’s rollup for all processes. This value can be misleading in that it includes shared pages and can therefore exceed the actual amount of memory being used by the processes. The _Total rollup can also mask processes that are leaking memory because other processes may be freeing memory thus creating a balance between leaked and freed memory. Identify processes that expand their working set over time for further analysis. Also, review handles and threads because both use resources and potentially can be mismanaged. After evaluating the process resource usage, you should be able to answer the following:  Are any of the processes increasing their private bytes over time?  Are any processes growing their working set over time?  Are any processes increasing the number of threads or handles over time?  Are any processes increasing their use of pool over time?  Is there a direct relationship between the above named resources and total committed memory or available memory?  If there is a relationship, is this normal behavior for the process in question? For example, SQL does not commit ‘min memory’ on startup; these pages are faulted in into the working set as needed. This is not necessarily an indication of a memory leak.  If there is clearly a leak in the overview and is not identifiable in the process counters it is most likely in the pool.  If the leak in pool is not associated with SQL Server handles, then more often than not, it is not a SQL Server issue. There is however the possibility that the leak could be associated with third party XPROCS, SP_OA* calls or OLDB providers. Review Paging Activity and Its Impact on CPU and I/O As stated earlier, paging is not in and of itself a bad thing. When starting a process the system faults in the pages of an executable, as they are needed. This is preferable to loading the entire image at startup. The same can be said for memory mapped files and file system cache. All of these features leverage the ability of the system to fault in pages as needed The greatest impact of paging on a process is when the process must wait for an in-page fault or when page file activity represents a significant portion of the disk activity on the disk the application is actively using. After evaluating page fault activity, you should be able to answer the following questions:  What is the relationship between PageFaults/sec and Page Input/sec + Page Output/Sec?  What is the relationship if any between hard page faults and available memory?  Does paging activity represent a significant portion of processor or I/O resource usage? Don’t Prematurely Jump to Any Conclusions Analyzing memory pressure takes time and patience. An individual counter in and of it self means little. It is only when you start to explore relationships between cause and effect that you can begin to understand the impact of a particular counter. The key thoughts to remember are:  With the exception of a swap (when the entire process’s working set has been swapped out/in), hard page faults to resolve reads, are the most expensive in terms its effect on a processes perceived performance.  In general, page writes associated with page faults do not directly affect a process’s perceived performance, unless that process is waiting on a free page to be made available. Page file activity can become a problem if that activity competes for a significant percentage of the disk throughput in a heavy I/O orientated environment. That assumes of course that the page file resides on the same disk the application is using. Lab 3.1 System Memory Lab 3.1 Analyzing System Memory Using System Monitor Exercise 1 – Troubleshooting the Cardinal1.log File Students will evaluate an existing System Monitor log and determine if there is a problem and what the problem is. Students should be able to isolate the issue as a memory problem, locate the offending process, and determine whether or not this is a pool issue. Exercise 2 – Leakyapp Behavior Students will start leaky app and monitor memory, page file and cache counters to better understand the dynamics of these counters. Exercise 3 – Process Swap Due To Minimizing of the Cmd Window Students will start SQL from command line while viewing SQL process performance counters. Students will then minimize the window and note the effect on the working set. Overview What You Will Learn After completing this lab, you will be able to:  Use some of the basic functions within System Monitor.  Troubleshoot one or more common performance scenarios. Before You Begin Prerequisites To complete this lab, you need the following:  Windows 2000  SQL Server 2000  Lab Files Provided  LeakyApp.exe (Resource Kit) Estimated time to complete this lab: 45 minutes Exercise 1 Troubleshooting the Cardinal1.log File In this exercise, you will analyze a log file from an actual system that was having performance problems. Like an actual support engineer, you will not have much information from which to draw conclusions. The customer has sent you this log file and it is up to you to find the cause of the problem. However, unlike the real world, you have an instructor available to give you hints should you become stuck. Goal Review the Cardinal1.log file (this file is from Windows NT 4.0 Performance Monitor, which Windows 2000 can read). Chart the log file and begin to investigate the counters to determine what is causing the performance problems. Your goal should be to isolate the problem to a major area such as pool, virtual address space etc, and begin to isolate the problem to a specific process or thread. This lab requires access to the log file Cardinal1.log located in C:\LABS\M3\LAB1\EX1  To analyze the log file 1. Using the Performance MMC, select the System Monitor snap-in, and click the View Log File Data button (icon looks like a disk). 2. Under Files of type, choose PERFMON Log Files (*.log) 3. Navigate to the folder containing Cardinal1.log file and open it. 4. Begin examining counters to find what might be causing the performance problems. When examining some of these counters, you may notice that some of them go off the top of the chart. It may be necessary to adjust the scale on these. This can be done by right-clicking the rightmost pane and selecting Properties. Select the Data tab. Select the counter that you wish to modify. Under the Scale option, change the scale value, which makes the counter data visible on the chart. You may need to experiment with different scale values before finding the ideal value. Also, it may sometimes be beneficial to adjust the vertical scale for the entire chart. Selecting the Graph tab on the Properties page can do this. In the Vertical scale area, adjust the Maximum and Minimum values to best fit the data on the chart. Lab 3.1, Exercise 1: Results Exercise 2 LeakyApp Behavior In this lab, you will have an opportunity to work with a partner to monitor a live system, which is suffering from a simulated memory leak. Goal During this lab, your goal is to observe the system behavior when memory starts to become a limited resource. Specifically you will want to monitor committed memory, available memory, the system working set including the file system cache and each processes working set. At the end of the lab, you should be able to provide an answer to the listed questions.  To monitor a live system with a memory leak 1. Choose one of the two systems as a victim on which to run the leakyapp.exe program. It is recommended that you boot using the \MAXMEM=128 option so that this lab goes a little faster. You and your partner should decide which server will play the role of the problematic server and which server is to be used for monitoring purposes. 2. On the problematic server, start the leakyapp program. 3. On the monitoring system, create a counter that logs all necessary counters need to troubleshoot a memory problem. This should include physicaldisk counters if you think paging is a problem. Because it is likely that you will only need to capture less than five minutes of activity, the suggested interval for capturing is five seconds. 4. After the counters have been started, start the leaky application program 5. Click Start Leaking. The button will now change to Stop Leaking, which indicates that the system is now leaking memory. 6. After leakyapp shows the page file is 50 percent full, click Stop leaking. Note that the process has not given back its memory, yet. After approximately one minute, exit. Lab 3.1, Exercise 2: Questions After analyzing the counter logs you should be able to answer the following: 1. Under which system memory counter does the leak show up clearly? Memory:Committed Bytes 2. What process counter looked very similar to the overall system counter that showed the leak? Private Bytes 3. Is the leak in Paged Pool, Non-paged pool, or elsewhere? Elsewhere 4. At what point did Windows 2000 start to aggressively trim the working sets of all user processes? <5 MB Free 5. Was the System Working Set trimmed before or after the working sets of other processes? After 6. What counter showed this? Memory:Cache Bytes 7. At what point was the File System Cache trimmed? After the first pass through all other working sets 8. What was the effect on all the processes working set when the application quit leaking? None 9. What was the effect on all the working sets when the application exited? Nothing, initially; but all grew fairly quickly based on use 10. When the server was running low on memory, which was Windows spending more time doing, paging to disk or in-paging? Paging to disk, initially; however, as other applications began to run, in-paging increased Exercise 3 Minimizing a Command Window In this exercise, you will have an opportunity to observe the behavior of Windows 2000 when a command window is minimized. Goal During this lab, your goal is to observe the behavior of Windows 2000 when a command window becomes minimized. Specifically, you will want to monitor private bytes, virtual bytes, and working set of SQL Server when the command window is minimized. At the end of the lab, you should be able to provide an answer to the listed questions.  To monitor a command window’s working set as the window is minimized 1. Using System Monitor, create a counter list that logs all necessary counters needed to troubleshoot a memory problem. Because it is likely that you will only need to capture less than five minutes of activity, the suggested capturing interval is five seconds. 2. After the counters have been started, start a Command Prompt window on the target system. 3. In the command window, start SQL Server from the command line. Example: SQL Servr.exe –c –sINSTANCE1 4. After SQL Server has successfully started, Minimize the Command Prompt window. 5. Wait approximately two minutes, and then Restore the window. 6. Wait approximately two minutes, and then stop the counter log. Lab 3.1, Exercise 3: Questions After analyzing the counter logs you should be able to answer the following questions: 1. What was the effect on SQL Servers private bytes, virtual bytes, and working set when the window was minimized? Private Bytes and Virtual Bytes remained the same, while Working Set went to 0 2. What was the effect on SQL Servers private bytes, virtual bytes, and working set when the window was restored? None; the Working Set did not grow until SQL accessed the pages and faulted them back in on an as-needed basis SQL Server Memory Overview SQL Server Memory Overview Now that you have a better understanding of how Windows 2000 manages memory resources, you can take a closer look at how SQL Server 2000 manages its memory. During the course of the lecture and labs you will have the opportunity to monitor SQL Servers use of memory under varying conditions using both System Monitor counters and SQL Server tools. SQL Server Memory Management Goals Because SQL Server has in-depth knowledge about the relationships between data and the pages they reside on, it is in a better position to judge when and what pages should be brought into memory, how many pages should be brought in at a time, and how long they should be resident. SQL Servers primary goals for management of its memory are the following:  Be able to dynamically adjust for varying amounts of available memory.  Be able to respond to outside memory pressure from other applications.  Be able to adjust memory dynamically for internal components. Items Covered  SQL Server Memory Definitions  SQL Server Memory Layout  SQL Server Memory Counters  Memory Configurations Options  Buffer Pool Performance and Counters  Set Aside Memory and Counters  General Troubleshooting Process  Memory Myths and Tips SQL Server Memory Definitions SQL Server Memory Definitions Pool A group of resources, objects, or logical components that can service a resource allocation request Cache The management of a pool or resource, the primary goal of which is to increase performance. Bpool The Bpool (Buffer Pool) is a single static class instance. The Bpool is made up of 8-KB buffers and can be used to handle data pages or external memory requests. There are three basic types or categories of committed memory in the Bpool.  Hashed Data Pages  Committed Buffers on the Free List  Buffers known by their owners (Refer to definition of Stolen) Consumer A consumer is a subsystem that uses the Bpool. A consumer can also be a provider to other consumers. There are five consumers and two advanced consumers who are responsible for the different categories of memory. The following list represents the consumers and a partial list of their categories  Connection – Responsible for PSS and ODS memory allocations  General – Resource structures, parse headers, lock manager objects  Utilities – Recovery, Log Manager  Optimizer – Query Optimization  Query Plan – Query Plan Storage Advanced Consumer Along with the five consumers, there are two advanced consumers. They are  Ccache – Procedure cache. Accepts plans from the Optimizer and Query Plan consumers. Is responsible for managing that memory and determines when to release the memory back to the Bpool.  Log Cache – Managed by the LogMgr, which uses the Utility consumer to coordinate memory requests with the Bpool. Reservation Requesting the future use of a resource. A reservation is a reasonable guarantee that the resource will be available in the future. Committed Producing the physical resource Allocation The act of providing the resource to a consumer Stolen The act of getting a buffer from the Bpool is referred to as stealing a buffer. If the buffer is stolen and hashed for a data page, it is referred to as, and counted as, a Hashed buffer, not a stolen buffer. Stolen buffers on the other hand are buffers used for things such as procedure cache and SRV_PROC structures. Target Target memory is the amount of memory SQL Server would like to maintain as committed memory. Target memory is based on the min and max server configuration values and current available memory as reported by the operating system. Actual target calculation is operating system specific. Memory to Leave (Set Aside) The virtual address space set aside to ensure there is sufficient address space for thread stacks, XPROCS, COM objects etc. Hashed Page A page in pool that represents a database page. SQL Server Memory Layout Virtual Address Space When SQL Server is started the minimum of physical ram or virtual address space supported by the OS is evaluated. There are many possible combinations of OS versions and memory configurations. For example: you could be running Microsoft Windows 2000 Advanced Server with 2 GB or possibly 4 GB of memory. To avoid page file use, the appropriate memory level is evaluated for each configuration. Important Utilities can inject a DLL into the process address space by using HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_DLLs When the USER32.dll library is mapped into the process space, so, too, are the DLLs listed in the Registry key. To determine what DLL’s are running in SQL Server address space you can use tlist.exe. You can also use a tool such as Depends from Microsoft or HandelEx from http://ww.sysinternals.com. Memory to Leave As stated earlier there are many possible configurations of physical memory and address space. It is possible for physical memory to be greater than virtual address space. To ensure that some virtual address space is always available for things such as thread stacks and external needs such as XPROCS, SQL Server reserves a small portion of virtual address space prior to determining the size of the buffer pool. This address space is referred to as Memory To Leave. Its size is based on the number of anticipated tread stacks and a default value for external needs referred to as cmbAddressSave. After reserving the buffer pool space, the Memory To Leave reservation is released. Buffer Pool Space During Startup, SQL Server must determine the maximum size of the buffer pool so that the BUF, BUFHASH and COMMIT BITMAP structures that are used to manage the Bpool can be created. It is important to understand that SQL Server does not take ‘max memory’ or existing memory pressure into consideration. The reserved address space of the buffer pool remains static for the life of SQL Server process. However, the committed space varies as necessary to provide dynamic scaling. Remember only the committed memory effects the overall memory usage on the machine. This ensures that the max memory configuration setting can be dynamically changed with minimal changes needed to the Bpool. The reserved space does not need to be adjusted and is maximized for the current machine configuration. Only the committed buffers need to be limited to maintain a specified max server memory (MB) setting. SQL Server Startup Pseudo Code The following pseudo code represents the process SQL Server goes through on startup. Warning This example does not represent a completely accurate portrayal of the steps SQL Server takes when initializing the buffer pool. Several details have been left out or glossed over. The intent of this example is to help you understand the general process, not the specific details.  Determine the size of cmbAddressSave (-g)  Determine Total Physical Memory  Determine Available Physical Memory  Determine Total Virtual Memory  Calculate MemToLeave maxworkterthreads * (stacksize=512 KB) + (cmbAddressSave = 256 MB)  Reserve MemToLeave and set PAGE_NOACCESS  Check for AWE, test to see if it makes sense to use it and log the results • Min(Available Memory, Max Server Memory) > Virtual Memory • Supports Read Scatter • SQL Server not started with -f • AWE Enabled via sp_configure • Enterprise Edition • Lock Pages In Memory user right enabled  Calculate Virtual Address Limit VA Limit = Min(Physical Memory, Virtual Memory – MemtoLeave)  Calculate the number of physical and virtual buffers that can be supported AWE Present Physical Buffers = (RAM / (PAGESIZE + Physical Overhead)) Virtual Buffers = (VA Limit / (PAGESIZE + Virtual Overhead)) AWE Not Present Physical Buffers = Virtual Buffers = VA Limit / (PAGESIZE + Physical Overhead + Virtual Overhead)  Make sure we have the minimum number of buffers Physical Buffers = Max(Physical Buffers, MIN_BUFFERS)  Allocate and commit the buffer management structures  Reserve the address space required to support the Bpool buffers  Release the MemToLeave SQL Server Startup Pseudo Code Example The following is an example based on the pseudo code represented on the previous page. This example is based on a machine with 384 MB of physical memory, not using AWE or /3GB. Note CmbAddressSave was changed between SQL Server 7.0 and SQL Server 2000. For SQL Server 7.0, cmbAddressSave was 128. Warning This example does not represent a completely accurate portrayal of the steps SQL Server takes when initializing the buffer pool. Several details have been left out or glossed over. The intent of this example is to help you understand the general process, not the specific details.  Determine the size of cmbAddressSave (No –g so 256MB)  Determine Total Physical Memory (384)  Determine Available Physical Memory (384)  Determine Total Virtual Memory (2GB)  Calculate MemToLeave maxworkterthreads * (stacksize=512 KB) + (cmbAddressSave = 256 MB) (255 * .5MB + 256MB = 384MB)  Reserve MemToLeave and set PAGE_NOACCESS  Check for AWE, test to see if it makes sense to use it and log the results (AWE Not Enabled)  Calculate Virtual Address Limit VA Limit = Min(Physical Memory, Virtual Memory – MemtoLeave) 384MB = Min(384MB, 2GB – 384MB)  Calculate the number of physical and virtual buffers that can be supported AWE Not Present 48664 (approx) = 384 MB / (8 KB + Overhead)  Make sure we have the minimum number of buffers Physical Buffers = Max(Physical Buffers, MIN_BUFFERS) 48664 = Max(48664,1024)  Allocate and commit the buffer management structures  Reserve the address space required to support the Bpool buffers  Release the MemToLeave Tip Trace Flag 1604 can be used to view memory allocations on startup. The cmbAddressSave can be adjusted using the –g XXX startup parameter. SQL Server Memory Counters SQL Server Memory Counters The two primary tools for monitoring and analyzing SQL Server memory usage are System Monitor and DBCC MEMORYSTATUS. For detailed information on DBCC MEMORYSTATUS refer to Q271624 Interpreting the Output of the DBCC MEMORYSTAUS Command. Important Represents SQL Server 2000 Counters. The counters presented are not the same as the counters for SQL Server 7.0. The SQL Server 7.0 counters are listed in the appendix. Determining Memory Usage for OS and BPOOL Memory Manager: Total Server memory (KB) - Represents all of SQL usage Buffer Manager: Total Pages - Represents total bpool usage To determine how much of Total Server Memory (KB) represents MemToLeave space; subtract Buffer Manager: Total Pages. The result can be verified against DBCC MEMORYSTATUS, specifically Dynamic Memory Manager: OS In Use. It should however be noted that this value only represents requests that went thru the bpool. Memory reserved outside of the bpool by components such as COM objects will not show up here, although they will count against SQL Server private byte count. Buffer Counts: Target (Buffer Manager: Target Pages) The size the buffer pool would like to be. If this value is larger than committed, the buffer pool is growing. Buffer Counts: Committed (Buffer Manager: Total Pages) The total number of buffers committed in the OS. This is the current size of the buffer pool. Buffer Counts: Min Free This is the number of pages that the buffer pool tries to keep on the free list. If the free list falls below this value, the buffer pool will attempt to populate it by discarding old pages from the data or procedure cache. Buffer Distribution: Free (Buffer Manager / Buffer Partition: Free Pages) This value represents the buffers currently not in use. These are available for data or may be requested by other components and mar

Computer Networking: A Top-Down Approach, 6th Edition Solutions to Review Questions and Problems Version Date: May 2012 This document contains the solutions to review questions and problems for the 5th edition of Computer Networking: A Top-Down Approach by Jim Kurose and Keith Ross. These solutions are being made available to instructors ONLY. Please do NOT copy or distribute this document to others (even other instructors). Please do not post any solutions on a publicly-available Web site. We’ll be happy to provide a copy (up-to-date) of this solution manual ourselves to anyone who asks. Acknowledgments: Over the years, several students and colleagues have helped us prepare this solutions manual. Special thanks goes to HongGang Zhang, Rakesh Kumar, Prithula Dhungel, and Vijay Annapureddy. Also thanks to all the readers who have made suggestions and corrected errors. All material © copyright 1996-2012 by J.F. Kurose and K.W. Ross. All rights reserved Chapter 1 Review Questions There is no difference. Throughout this text, the words “host” and “end system” are used interchangeably. End systems include PCs, workstations, Web servers, mail servers, PDAs, Internet-connected game consoles, etc. From Wikipedia: Diplomatic protocol is commonly described as a set of international courtesy rules. These well-established and time-honored rules have made it easier for nations and people to live and work together. Part of protocol has always been the acknowledgment of the hierarchical standing of all present. Protocol rules are based on the principles of civility. Standards are important for protocols so that people can create networking systems and products that interoperate. 1. Dial-up modem over telephone line: home; 2. DSL over telephone line: home or small office; 3. Cable to HFC: home; 4. 100 Mbps switched Ethernet: enterprise; 5. Wifi (802.11): home and enterprise: 6. 3G and 4G: wide-area wireless. HFC bandwidth is shared among the users. On the downstream channel, all packets emanate from a single source, namely, the head end. Thus, there are no collisions in the downstream channel. In most American cities, the current possibilities include: dial-up; DSL; cable modem; fiber-to-the-home. 7. Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps and 10 Gbps. 8. Today, Ethernet most commonly runs over twisted-pair copper wire. It also can run over fibers optic links. 9. Dial up modems: up to 56 Kbps, bandwidth is dedicated; ADSL: up to 24 Mbps downstream and 2.5 Mbps upstream, bandwidth is dedicated; HFC, rates up to 42.8 Mbps and upstream rates of up to 30.7 Mbps, bandwidth is shared. FTTH: 2-10Mbps upload; 10-20 Mbps download; bandwidth is not shared. 10. There are two popular wireless Internet access technologies today: Wifi (802.11) In a wireless LAN, wireless users transmit/receive packets to/from an base station (i.e., wireless access point) within a radius of few tens of meters. The base station is typically connected to the wired Internet and thus serves to connect wireless users to the wired network. 3G and 4G wide-area wireless access networks. In these systems, packets are transmitted over the same wireless infrastructure used for cellular telephony, with the base station thus being managed by a telecommunications provider. This provides wireless access to users within a radius of tens of kilometers of the base station. 11. At time t0 the sending host begins to transmit. At time t1 = L/R1, the sending host completes transmission and the entire packet is received at the router (no propagation delay). Because the router has the entire packet at time t1, it can begin to transmit the packet to the receiving host at time t1. At time t2 = t1 + L/R2, the router completes transmission and the entire packet is received at the receiving host (again, no propagation delay). Thus, the end-to-end delay is L/R1 + L/R2. 12. A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth. FDM requires sophisticated analog hardware to shift signal into appropriate frequency bands. 13. a) 2 users can be supported because each user requires half of the link bandwidth. b) Since each user requires 1Mbps when transmitting, if two or fewer users transmit simultaneously, a maximum of 2Mbps will be required. Since the available bandwidth of the shared link is 2Mbps, there will be no queuing delay before the link. Whereas, if three users transmit simultaneously, the bandwidth required will be 3Mbps which is more than the available bandwidth of the shared link. In this case, there will be queuing delay before the link. c) Probability that a given user is transmitting = 0.2 d) Probability that all three users are transmitting simultaneously = = (0.2)3 = 0.008. Since the queue grows when all the users are transmitting, the fraction of time during which the queue grows (which is equal to the probability that all three users are transmitting simultaneously) is 0.008. 14. If the two ISPs do not peer with each other, then when they send traffic to each other they have to send the traffic through a provider ISP (intermediary), to which they have to pay for carrying the traffic. By peering with each other directly, the two ISPs can reduce their payments to their provider ISPs. An Internet Exchange Points (IXP) (typically in a standalone building with its own switches) is a meeting point where multiple ISPs can connect and/or peer together. An ISP earns its money by charging each of the the ISPs that connect to the IXP a relatively small fee, which may depend on the amount of traffic sent to or received from the IXP. 15. Google's private network connects together all its data centers, big and small. Traffic between the Google data centers passes over its private network rather than over the public Internet. Many of these data centers are located in, or close to, lower tier ISPs. Therefore, when Google delivers content to a user, it often can bypass higher tier ISPs. What motivates content providers to create these networks? First, the content provider has more control over the user experience, since it has to use few intermediary ISPs. Second, it can save money by sending less traffic into provider networks. Third, if ISPs decide to charge more money to highly profitable content providers (in countries where net neutrality doesn't apply), the content providers can avoid these extra payments. 16. The delay components are processing delays, transmission delays, propagation delays, and queuing delays. All of these delays are fixed, except for the queuing delays, which are variable. 17. a) 1000 km, 1 Mbps, 100 bytes b) 100 km, 1 Mbps, 100 bytes 18. 10msec; d/s; no; no 19. a) 500 kbps b) 64 seconds c) 100kbps; 320 seconds 20. End system A breaks the large file into chunks. It adds header to each chunk, thereby generating multiple packets from the file. The header in each packet includes the IP address of the destination (end system B). The packet switch uses the destination IP address in the packet to determine the outgoing link. Asking which road to take is analogous to a packet asking which outgoing link it should be forwarded on, given the packet’s destination address. 21. The maximum emission rate is 500 packets/sec and the maximum transmission rate is 350 packets/sec. The corresponding traffic intensity is 500/350 =1.43 > 1. Loss will eventually occur for each experiment; but the time when loss first occurs will be different from one experiment to the next due to the randomness in the emission process. 22. Five generic tasks are error control, flow control, segmentation and reassembly, multiplexing, and connection setup. Yes, these tasks can be duplicated at different layers. For example, error control is often provided at more than one layer. 23. The five layers in the Internet protocol stack are – from top to bottom – the application layer, the transport layer, the network layer, the link layer, and the physical layer. The principal responsibilities are outlined in Section 1.5.1. 24. Application-layer message: data which an application wants to send and passed onto the transport layer; transport-layer segment: generated by the transport layer and encapsulates application-layer message with transport layer header; network-layer datagram: encapsulates transport-layer segment with a network-layer header; link-layer frame: encapsulates network-layer datagram with a link-layer header. 25. Routers process network, link and physical layers (layers 1 through 3). (This is a little bit of a white lie, as modern routers sometimes act as firewalls or caching components, and process Transport layer as well.) Link layer switches process link and physical layers (layers 1 through2). Hosts process all five layers. 26. a) Virus Requires some form of human interaction to spread. Classic example: E-mail viruses. b) Worms No user replication needed. Worm in infected host scans IP addresses and port numbers, looking for vulnerable processes to infect. 27. Creation of a botnet requires an attacker to find vulnerability in some application or system (e.g. exploiting the buffer overflow vulnerability that might exist in an application). After finding the vulnerability, the attacker needs to scan for hosts that are vulnerable. The target is basically to compromise a series of systems by exploiting that particular vulnerability. Any system that is part of the botnet can automatically scan its environment and propagate by exploiting the vulnerability. An important property of such botnets is that the originator of the botnet can remotely control and issue commands to all the nodes in the botnet. Hence, it becomes possible for the attacker to issue a command to all the nodes, that target a single node (for example, all nodes in the botnet might be commanded by the attacker to send a TCP SYN message to the target, which might result in a TCP SYN flood attack at the target). 28. Trudy can pretend to be Bob to Alice (and vice-versa) and partially or completely modify the message(s) being sent from Bob to Alice. For example, she can easily change the phrase “Alice, I owe you $1000” to “Alice, I owe you $10,000”. Furthermore, Trudy can even drop the packets that are being sent by Bob to Alice (and vise-versa), even if the packets from Bob to Alice are encrypted. Chapter 1 Problems Problem 1 There is no single right answer to this question. Many protocols would do the trick. Here's a simple answer below: Messages from ATM machine to Server Msg name purpose -------- ------- HELO Let server know that there is a card in the ATM machine ATM card transmits user ID to Server PASSWD User enters PIN, which is sent to server BALANCE User requests balance WITHDRAWL User asks to withdraw money BYE user all done Messages from Server to ATM machine (display) Msg name purpose -------- ------- PASSWD Ask user for PIN (password) OK last requested operation (PASSWD, WITHDRAWL) OK ERR last requested operation (PASSWD, WITHDRAWL) in ERROR AMOUNT sent in response to BALANCE request BYE user done, display welcome screen at ATM Correct operation: client server HELO (userid) --------------> (check if valid userid) <------------- PASSWD PASSWD --------------> (check password) <------------- AMOUNT WITHDRAWL --------------> check if enough $ to cover withdrawl (check if valid userid) <------------- PASSWD PASSWD --------------> (check password) <------------- AMOUNT WITHDRAWL --------------> check if enough $ to cover withdrawl <------------- BYE Problem 2 At time N*(L/R) the first packet has reached the destination, the second packet is stored in the last router, the third packet is stored in the next-to-last router, etc. At time N*(L/R) + L/R, the second packet has reached the destination, the third packet is stored in the last router, etc. Continuing with this logic, we see that at time N*(L/R) + (P-1)*(L/R) = (N+P-1)*(L/R) all packets have reached the destination. Problem 3 a) A circuit-switched network would be well suited to the application, because the application involves long sessions with predictable smooth bandwidth requirements. Since the transmission rate is known and not bursty, bandwidth can be reserved for each application session without significant waste. In addition, the overhead costs of setting up and tearing down connections are amortized over the lengthy duration of a typical application session. b) In the worst case, all the applications simultaneously transmit over one or more network links. However, since each link has sufficient bandwidth to handle the sum of all of the applications' data rates, no congestion (very little queuing) will occur. Given such generous link capacities, the network does not need congestion control mechanisms. Problem 4 Between the switch in the upper left and the switch in the upper right we can have 4 connections. Similarly we can have four connections between each of the 3 other pairs of adjacent switches. Thus, this network can support up to 16 connections. We can 4 connections passing through the switch in the upper-right-hand corner and another 4 connections passing through the switch in the lower-left-hand corner, giving a total of 8 connections. Yes. For the connections between A and C, we route two connections through B and two connections through D. For the connections between B and D, we route two connections through A and two connections through C. In this manner, there are at most 4 connections passing through any link. Problem 5 Tollbooths are 75 km apart, and the cars propagate at 100km/hr. A tollbooth services a car at a rate of one car every 12 seconds. a) There are ten cars. It takes 120 seconds, or 2 minutes, for the first tollbooth to service the 10 cars. Each of these cars has a propagation delay of 45 minutes (travel 75 km) before arriving at the second tollbooth. Thus, all the cars are lined up before the second tollbooth after 47 minutes. The whole process repeats itself for traveling between the second and third tollbooths. It also takes 2 minutes for the third tollbooth to service the 10 cars. Thus the total delay is 96 minutes. b) Delay between tollbooths is 8*12 seconds plus 45 minutes, i.e., 46 minutes and 36 seconds. The total delay is twice this amount plus 8*12 seconds, i.e., 94 minutes and 48 seconds. Problem 6 a) seconds. b) seconds. c) seconds. d) The bit is just leaving Host A. e) The first bit is in the link and has not reached Host B. f) The first bit has reached Host B. g) Want km. Problem 7 Consider the first bit in a packet. Before this bit can be transmitted, all of the bits in the packet must be generated. This requires sec=7msec. The time required to transmit the packet is sec= sec. Propagation delay = 10 msec. The delay until decoding is 7msec + sec + 10msec = 17.224msec A similar analysis shows that all bits experience a delay of 17.224 msec. Problem 8 a) 20 users can be supported. b) . c) . d) . We use the central limit theorem to approximate this probability. Let be independent random variables such that . “21 or more users” when is a standard normal r.v. Thus “21 or more users” . Problem 9 10,000 Problem 10 The first end system requires L/R1 to transmit the packet onto the first link; the packet propagates over the first link in d1/s1; the packet switch adds a processing delay of dproc; after receiving the entire packet, the packet switch connecting the first and the second link requires L/R2 to transmit the packet onto the second link; the packet propagates over the second link in d2/s2. Similarly, we can find the delay caused by the second switch and the third link: L/R3, dproc, and d3/s3. Adding these five delays gives dend-end = L/R1 + L/R2 + L/R3 + d1/s1 + d2/s2 + d3/s3+ dproc+ dproc To answer the second question, we simply plug the values into the equation to get 6 + 6 + 6 + 20+16 + 4 + 3 + 3 = 64 msec. Problem 11 Because bits are immediately transmitted, the packet switch does not introduce any delay; in particular, it does not introduce a transmission delay. Thus, dend-end = L/R + d1/s1 + d2/s2+ d3/s3 For the values in Problem 10, we get 6 + 20 + 16 + 4 = 46 msec. Problem 12 The arriving packet must first wait for the link to transmit 4.5 *1,500 bytes = 6,750 bytes or 54,000 bits. Since these bits are transmitted at 2 Mbps, the queuing delay is 27 msec. Generally, the queuing delay is (nL + (L - x))/R. Problem 13 The queuing delay is 0 for the first transmitted packet, L/R for the second transmitted packet, and generally, (n-1)L/R for the nth transmitted packet. Thus, the average delay for the N packets is: (L/R + 2L/R + ....... + (N-1)L/R)/N = L/(RN) * (1 + 2 + ..... + (N-1)) = L/(RN) * N(N-1)/2 = LN(N-1)/(2RN) = (N-1)L/(2R) Note that here we used the well-known fact: 1 + 2 + ....... + N = N(N+1)/2 It takes seconds to transmit the packets. Thus, the buffer is empty when a each batch of packets arrive. Thus, the average delay of a packet across all batches is the average delay within one batch, i.e., (N-1)L/2R. Problem 14 The transmission delay is . The total delay is Let . Total delay = For x=0, the total delay =0; as we increase x, total delay increases, approaching infinity as x approaches 1/a. Problem 15 Total delay . Problem 16 The total number of packets in the system includes those in the buffer and the packet that is being transmitted. So, N=10+1. Because , so (10+1)=a*(queuing delay + transmission delay). That is, 11=a*(0.01+1/100)=a*(0.01+0.01). Thus, a=550 packets/sec. Problem 17 There are nodes (the source host and the routers). Let denote the processing delay at the th node. Let be the transmission rate of the th link and let . Let be the propagation delay across the th link. Then . Let denote the average queuing delay at node . Then . Problem 18 On linux you can use the command traceroute www.targethost.com and in the Windows command prompt you can use tracert www.targethost.com In either case, you will get three delay measurements. For those three measurements you can calculate the mean and standard deviation. Repeat the experiment at different times of the day and comment on any changes. Here is an example solution: Traceroutes between San Diego Super Computer Center and www.poly.edu The average (mean) of the round-trip delays at each of the three hours is 71.18 ms, 71.38 ms and 71.55 ms, respectively. The standard deviations are 0.075 ms, 0.21 ms, 0.05 ms, respectively. In this example, the traceroutes have 12 routers in the path at each of the three hours. No, the paths didn’t change during any of the hours. Traceroute packets passed through four ISP networks from source to destination. Yes, in this experiment the largest delays occurred at peering interfaces between adjacent ISPs. Traceroutes from www.stella-net.net (France) to www.poly.edu (USA). The average round-trip delays at each of the three hours are 87.09 ms, 86.35 ms and 86.48 ms, respectively. The standard deviations are 0.53 ms, 0.18 ms, 0.23 ms, respectively. In this example, there are 11 routers in the path at each of the three hours. No, the paths didn’t change during any of the hours. Traceroute packets passed three ISP networks from source to destination. Yes, in this experiment the largest delays occurred at peering interfaces between adjacent ISPs. Problem 19 An example solution: Traceroutes from two different cities in France to New York City in United States In these traceroutes from two different cities in France to the same destination host in United States, seven links are in common including the transatlantic link. In this example of traceroutes from one city in France and from another city in Germany to the same host in United States, three links are in common including the transatlantic link. Traceroutes to two different cities in China from same host in United States Five links are common in the two traceroutes. The two traceroutes diverge before reaching China Problem 20 Throughput = min{Rs, Rc, R/M} Problem 21 If only use one path, the max throughput is given by: . If use all paths, the max throughput is given by . Problem 22 Probability of successfully receiving a packet is: ps= (1-p)N. The number of transmissions needed to be performed until the packet is successfully received by the client is a geometric random variable with success probability ps. Thus, the average number of transmissions needed is given by: 1/ps . Then, the average number of re-transmissions needed is given by: 1/ps -1. Problem 23 Let’s call the first packet A and call the second packet B. If the bottleneck link is the first link, then packet B is queued at the first link waiting for the transmission of packet A. So the packet inter-arrival time at the destination is simply L/Rs. If the second link is the bottleneck link and both packets are sent back to back, it must be true that the second packet arrives at the input queue of the second link before the second link finishes the transmission of the first packet. That is, L/Rs + L/Rs + dprop = L/Rs + dprop + L/Rc Thus, the minimum value of T is L/Rc  L/Rs . Problem 24 40 terabytes = 40 * 1012 * 8 bits. So, if using the dedicated link, it will take 40 * 1012 * 8 / (100 *106 ) =3200000 seconds = 37 days. But with FedEx overnight delivery, you can guarantee the data arrives in one day, and it should cost less than $100. Problem 25 160,000 bits 160,000 bits The bandwidth-delay product of a link is the maximum number of bits that can be in the link. the width of a bit = length of link / bandwidth-delay product, so 1 bit is 125 meters long, which is longer than a football field s/R Problem 26 s/R=20000km, then R=s/20000km= 2.5*108/(2*107)= 12.5 bps Problem 27 80,000,000 bits 800,000 bits, this is because that the maximum number of bits that will be in the link at any given time = min(bandwidth delay product, packet size) = 800,000 bits. .25 meters Problem 28 ttrans + tprop = 400 msec + 80 msec = 480 msec. 20 * (ttrans + 2 tprop) = 20*(20 msec + 80 msec) = 2 sec. Breaking up a file takes longer to transmit because each data packet and its corresponding acknowledgement packet add their own propagation delays. Problem 29 Recall geostationary satellite is 36,000 kilometers away from earth surface. 150 msec 1,500,000 bits 600,000,000 bits Problem 30 Let’s suppose the passenger and his/her bags correspond to the data unit arriving to the top of the protocol stack. When the passenger checks in, his/her bags are checked, and a tag is attached to the bags and ticket. This is additional information added in the Baggage layer if Figure 1.20 that allows the Baggage layer to implement the service or separating the passengers and baggage on the sending side, and then reuniting them (hopefully!) on the destination side. When a passenger then passes through security and additional stamp is often added to his/her ticket, indicating that the passenger has passed through a security check. This information is used to ensure (e.g., by later checks for the security information) secure transfer of people. Problem 31 Time to send message from source host to first packet switch = With store-and-forward switching, the total time to move message from source host to destination host = Time to send 1st packet from source host to first packet switch = . . Time at which 2nd packet is received at the first switch = time at which 1st packet is received at the second switch = Time at which 1st packet is received at the destination host = . After this, every 5msec one packet will be received; thus time at which last (800th) packet is received = . It can be seen that delay in using message segmentation is significantly less (almost 1/3rd). Without message segmentation, if bit errors are not tolerated, if there is a single bit error, the whole message has to be retransmitted (rather than a single packet). Without message segmentation, huge packets (containing HD videos, for example) are sent into the network. Routers have to accommodate these huge packets. Smaller packets have to queue behind enormous packets and suffer unfair delays. Packets have to be put in sequence at the destination. Message segmentation results in many smaller packets. Since header size is usually the same for all packets regardless of their size, with message segmentation the total amount of header bytes is more. Problem 32 Yes, the delays in the applet correspond to the delays in the Problem 31.The propagation delays affect the overall end-to-end delays both for packet switching and message switching equally. Problem 33 There are F/S packets. Each packet is S=80 bits. Time at which the last packet is received at the first router is sec. At this time, the first F/S-2 packets are at the destination, and the F/S-1 packet is at the second router. The last packet must then be transmitted by the first router and the second router, with each transmission taking sec. Thus delay in sending the whole file is To calculate the value of S which leads to the minimum delay, Problem 34 The circuit-switched telephone networks and the Internet are connected together at "gateways". When a Skype user (connected to the Internet) calls an ordinary telephone, a circuit is established between a gateway and the telephone user over the circuit switched network. The skype user's voice is sent in packets over the Internet to the gateway. At the gateway, the voice signal is reconstructed and then sent over the circuit. In the other direction, the voice signal is sent over the circuit switched network to the gateway. The gateway packetizes the voice signal and sends the voice packets to the Skype user. Chapter 2 Review Questions The Web: HTTP; file transfer: FTP; remote login: Telnet; e-mail: SMTP; BitTorrent file sharing: BitTorrent protocol Network architecture refers to the organization of the communication process into layers (e.g., the five-layer Internet architecture). Application architecture, on the other hand, is designed by an application developer and dictates the broad structure of the application (e.g., client-server or P2P). The process which initiates the communication is the client; the process that waits to be contacted is the server. No. In a P2P file-sharing application, the peer that is receiving a file is typically the client and the peer that is sending the file is typically the server. The IP address of the destination host and the port number of the socket in the destination process. You would use UDP. With UDP, the transaction can be completed in one roundtrip time (RTT) - the client sends the transaction request into a UDP socket, and the server sends the reply back to the client's UDP socket. With TCP, a minimum of two RTTs are needed - one to set-up the TCP connection, and another for the client to send the request, and for the server to send back the reply. One such example is remote word processing, for example, with Google docs. However, because Google docs runs over the Internet (using TCP), timing guarantees are not provided. a) Reliable data transfer TCP provides a reliable byte-stream between client and server but UDP does not. b) A guarantee that a certain value for throughput will be maintained Neither c) A guarantee that data will be delivered within a specified amount of time Neither d) Confidentiality (via encryption) Neither SSL operates at the application layer. The SSL socket takes unencrypted data from the application layer, encrypts it and then passes it to the TCP socket. If the application developer wants TCP to be enhanced with SSL, she has to include the SSL code in the application. A protocol uses handshaking if the two communicating entities first exchange control packets before sending data to each other. SMTP uses handshaking at the application layer whereas HTTP does not. The applications associated with those protocols require that all application data be received in the correct order and without gaps. TCP provides this service whereas UDP does not. When the user first visits the site, the server creates a unique identification number, creates an entry in its back-end database, and returns this identification number as a cookie number. This cookie number is stored on the user’s host and is managed by the browser. During each subsequent visit (and purchase), the browser sends the cookie number back to the site. Thus the site knows when this user (more precisely, this browser) is visiting the site. Web caching can bring the desired content “closer” to the user, possibly to the same LAN to which the user’s host is connected. Web caching can reduce the delay for all objects, even objects that are not cached, since caching reduces the traffic on links. Telnet is not available in Windows 7 by default. to make it available, go to Control Panel, Programs and Features, Turn Windows Features On or Off, Check Telnet client. To start Telnet, in Windows command prompt, issue the following command > telnet webserverver 80 where "webserver" is some webserver. After issuing the command, you have established a TCP connection between your client telnet program and the web server. Then type in an HTTP GET message. An example is given below: Since the index.html page in this web server was not modified since Fri, 18 May 2007 09:23:34 GMT, and the above commands were issued on Sat, 19 May 2007, the server returned "304 Not Modified". Note that the first 4 lines are the GET message and header lines inputed by the user, and the next 4 lines (starting from HTTP/1.1 304 Not Modified) is the response from the web server. FTP uses two parallel TCP connections, one connection for sending control information (such as a request to transfer a file) and another connection for actually transferring the file. Because the control information is not sent over the same connection that the file is sent over, FTP sends control information out of band. The message is first sent from Alice’s host to her mail server over HTTP. Alice’s mail server then sends the message to Bob’s mail server over SMTP. Bob then transfers the message from his mail server to his host over POP3. 17. Received: from 65.54.246.203 (EHLO bay0-omc3-s3.bay0.hotmail.com) (65.54.246.203) by mta419.mail.mud.yahoo.com with SMTP; Sat, 19 May 2007 16:53:51 -0700 Received: from hotmail.com ([65.55.135.106]) by bay0-omc3-s3.bay0.hotmail.com with Microsoft SMTPSVC(6.0.3790.2668); Sat, 19 May 2007 16:52:42 -0700 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Sat, 19 May 2007 16:52:41 -0700 Message-ID: Received: from 65.55.135.123 by by130fd.bay130.hotmail.msn.com with HTTP; Sat, 19 May 2007 23:52:36 GMT From: "prithula dhungel" To: prithula@yahoo.com Bcc: Subject: Test mail Date: Sat, 19 May 2007 23:52:36 +0000 Mime-Version: 1.0 Content-Type: Text/html; format=flowed Return-Path: prithuladhungel@hotmail.com Figure: A sample mail message header Received: This header field indicates the sequence in which the SMTP servers send and receive the mail message including the respective timestamps. In this example there are 4 “Received:” header lines. This means the mail message passed through 5 different SMTP servers before being delivered to the receiver’s mail box. The last (forth) “Received:” header indicates the mail message flow from the SMTP server of the sender to the second SMTP server in the chain of servers. The sender’s SMTP server is at address 65.55.135.123 and the second SMTP server in the chain is by130fd.bay130.hotmail.msn.com. The third “Received:” header indicates the mail message flow from the second SMTP server in the chain to the third server, and so on. Finally, the first “Received:” header indicates the flow of the mail messages from the forth SMTP server to the last SMTP server (i.e. the receiver’s mail server) in the chain. Message-id: The message has been given this number BAY130-F26D9E35BF59E0D18A819AFB9310@phx.gbl (by bay0-omc3-s3.bay0.hotmail.com. Message-id is a unique string assigned by the mail system when the message is first created. From: This indicates the email address of the sender of the mail. In the given example, the sender is “prithuladhungel@hotmail.com” To: This field indicates the email address of the receiver of the mail. In the example, the receiver is “prithula@yahoo.com” Subject: This gives the subject of the mail (if any specified by the sender). In the example, the subject specified by the sender is “Test mail” Date: The date and time when the mail was sent by the sender. In the example, the sender sent the mail on 19th May 2007, at time 23:52:36 GMT. Mime-version: MIME version used for the mail. In the example, it is 1.0. Content-type: The type of content in the body of the mail message. In the example, it is “text/html”. Return-Path: This specifies the email address to which the mail will be sent if the receiver of this mail wants to reply to the sender. This is also used by the sender’s mail server for bouncing back undeliverable mail messages of mailer-daemon error messages. In the example, the return path is “prithuladhungel@hotmail.com”. With download and delete, after a user retrieves its messages from a POP server, the messages are deleted. This poses a problem for the nomadic user, who may want to access the messages from many different machines (office PC, home PC, etc.). In the download and keep configuration, messages are not deleted after the user retrieves the messages. This can also be inconvenient, as each time the user retrieves the stored messages from a new machine, all of non-deleted messages will be transferred to the new machine (including very old messages). Yes an organization’s mail server and Web server can have the same alias for a host name. The MX record is used to map the mail server’s host name to its IP address. You should be able to see the sender's IP address for a user with an .edu email address. But you will not be able to see the sender's IP address if the user uses a gmail account. It is not necessary that Bob will also provide chunks to Alice. Alice has to be in the top 4 neighbors of Bob for Bob to send out chunks to her; this might not occur even if Alice provides chunks to Bob throughout a 30-second interval. Recall that in BitTorrent, a peer picks a random peer and optimistically unchokes the peer for a short period of time. Therefore, Alice will eventually be optimistically unchoked by one of her neighbors, during which time she will receive chunks from that neighbor. The overlay network in a P2P file sharing system consists of the nodes participating in the file sharing system and the logical links between the nodes. There is a logical link (an “edge” in graph theory terms) from node A to node B if there is a semi-permanent TCP connection between A and B. An overlay network does not include routers. Mesh DHT: The advantage is in order to a route a message to the peer (with ID) that is closest to the key, only one hop is required; the disadvantage is that each peer must track all other peers in the DHT. Circular DHT: the advantage is that each peer needs to track only a few other peers; the disadvantage is that O(N) hops are needed to route a message to the peer that is closest to the key. 25. File Distribution Instant Messaging Video Streaming Distributed Computing With the UDP server, there is no welcoming socket, and all data from different clients enters the server through this one socket. With the TCP server, there is a welcoming socket, and each time a client initiates a connection to the server, a new socket is created. Thus, to support n simultaneous connections, the server would need n+1 sockets. For the TCP application, as soon as the client is executed, it attempts to initiate a TCP connection with the server. If the TCP server is not running, then the client will fail to make a connection. For the UDP application, the client does not initiate connections (or attempt to communicate with the UDP server) immediately upon execution Chapter 2 Problems Problem 1 a) F b) T c) F d) F e) F Problem 2 Access control commands: USER, PASS, ACT, CWD, CDUP, SMNT, REIN, QUIT. Transfer parameter commands: PORT, PASV, TYPE STRU, MODE. Service commands: RETR, STOR, STOU, APPE, ALLO, REST, RNFR, RNTO, ABOR, DELE, RMD, MRD, PWD, LIST, NLST, SITE, SYST, STAT, HELP, NOOP. Problem 3 Application layer protocols: DNS and HTTP Transport layer protocols: UDP for DNS; TCP for HTTP Problem 4 The document request was http://gaia.cs.umass.edu/cs453/index.html. The Host : field indicates the server's name and /cs453/index.html indicates the file name. The browser is running HTTP version 1.1, as indicated just before the first pair. The browser is requesting a persistent connection, as indicated by the Connection: keep-alive. This is a trick question. This information is not contained in an HTTP message anywhere. So there is no way to tell this from looking at the exchange of HTTP messages alone. One would need information from the IP datagrams (that carried the TCP segment that carried the HTTP GET request) to answer this question. Mozilla/5.0. The browser type information is needed by the server to send different versions of the same object to different types of browsers. Problem 5 The status code of 200 and the phrase OK indicate that the server was able to locate the document successfully. The reply was provided on Tuesday, 07 Mar 2008 12:39:45 Greenwich Mean Time. The document index.html was last modified on Saturday 10 Dec 2005 18:27:46 GMT. There are 3874 bytes in the document being returned. The first five bytes of the returned document are : server agreed to a persistent connection, as indicated by the Connection: Keep-Alive field Problem 6 Persistent connections are discussed in section 8 of RFC 2616 (the real goal of this question was to get you to retrieve and read an RFC). Sections 8.1.2 and 8.1.2.1 of the RFC indicate that either the client or the server can indicate to the other that it is going to close the persistent connection. It does so by including the connection-token "close" in the Connection-header field of the http request/reply. HTTP does not provide any encryption services. (From RFC 2616) “Clients that use persistent connections should limit the number of simultaneous connections that they maintain to a given server. A single-user client SHOULD NOT maintain more than 2 connections with any server or proxy.” Yes. (From RFC 2616) “A client might have started to send a new request at the same time that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed while it was idle, but from the client's point of view, a request is in progress.” Problem 7 The total amount of time to get the IP address is . Once the IP address is known, elapses to set up the TCP connection and another elapses to request and receive the small object. The total response time is Problem 8 . . Problem 9 The time to transmit an object of size L over a link or rate R is L/R. The average time is the average size of the object divided by R:  = (850,000 bits)/(15,000,000 bits/sec) = .0567 sec The traffic intensity on the link is given by =(16 requests/sec)(.0567 sec/request) = 0.907. Thus, the average access delay is (.0567 sec)/(1 - .907)  .6 seconds. The total average response time is therefore .6 sec + 3 sec = 3.6 sec. The traffic intensity on the access link is reduced by 60% since the 60% of the requests are satisfied within the institutional network. Thus the average access delay is (.0567 sec)/[1 – (.4)(.907)] = .089 seconds. The response time is approximately zero if the request is satisfied by the cache (which happens with probability .6); the average response time is .089 sec + 3 sec = 3.089 sec for cache misses (which happens 40% of the time). So the average response time is (.6)(0 sec) + (.4)(3.089 sec) = 1.24 seconds. Thus the average response time is reduced from 3.6 sec to 1.24 sec. Problem 10 Note that each downloaded object can be completely put into one data packet. Let Tp denote the one-way propagation delay between the client and the server. First consider parallel downloads using non-persistent connections. Parallel downloads would allow 10 connections to share the 150 bits/sec bandwidth, giving each just 15 bits/sec. Thus, the total time needed to receive all objects is given by: (200/150+Tp + 200/150 +Tp + 200/150+Tp + 100,000/150+ Tp ) + (200/(150/10)+Tp + 200/(150/10) +Tp + 200/(150/10)+Tp + 100,000/(150/10)+ Tp ) = 7377 + 8*Tp (seconds) Now consider a persistent HTTP connection. The total time needed is given by: (200/150+Tp + 200/150 +Tp + 200/150+Tp + 100,000/150+ Tp ) + 10*(200/150+Tp + 100,000/150+ Tp ) =7351 + 24*Tp (seconds) Assuming the speed of light is 300*106 m/sec, then Tp=10/(300*106)=0.03 microsec. Tp is therefore negligible compared with transmission delay. Thus, we see that persistent HTTP is not significantly faster (less than 1 percent) than the non-persistent case with parallel download. Problem 11 Yes, because Bob has more connections, he can get a larger share of the link bandwidth. Yes, Bob still needs to perform parallel downloads; otherwise he will get less bandwidth than the other four users. Problem 12 Server.py from socket import * serverPort=12000 serverSocket=socket(AF_INET,SOCK_STREAM) serverSocket.bind(('',serverPort)) serverSocket.listen(1) connectionSocket, addr = serverSocket.accept() while 1: sentence = connectionSocket.recv(1024) print 'From Server:', sentence, '\n' serverSocket.close() Problem 13 The MAIL FROM: in SMTP is a message from the SMTP client that identifies the sender of the mail message to the SMTP server. The From: on the mail message itself is NOT an SMTP message, but rather is just a line in the body of the mail message. Problem 14 SMTP uses a line containing only a period to mark the end of a message body. HTTP uses “Content-Length header field” to indicate the length of a message body. No, HTTP cannot use the method used by SMTP, because HTTP message could be binary data, whereas in SMTP, the message body must be in 7-bit ASCII format. Problem 15 MTA stands for Mail Transfer Agent. A host sends the message to an MTA. The message then follows a sequence of MTAs to reach the receiver’s mail reader. We see that this spam message follows a chain of MTAs. An honest MTA should report where it receives the message. Notice that in this message, “asusus-4b96 ([58.88.21.177])” does not report from where it received the email. Since we assume only the originator is dishonest, so “asusus-4b96 ([58.88.21.177])” must be the originator. Problem 16 UIDL abbreviates “unique-ID listing”. When a POP3 client issues the UIDL command, the server responds with the unique message ID for all of the messages present in the user's mailbox. This command is useful for “download and keep”. By maintaining a file that lists the messages retrieved during earlier sessions, the client can use the UIDL command to determine which messages on the server have already been seen. Problem 17 a) C: dele 1 C: retr 2 S: (blah blah … S: ………..blah) S: . C: dele 2 C: quit S: +OK POP3 server signing off b) C: retr 2 S: blah blah … S: ………..blah S: . C: quit S: +OK POP3 server signing off C: list S: 1 498 S: 2 912 S: . C: retr 1 S: blah ….. S: ….blah S: . C: retr 2 S: blah blah … S: ………..blah S: . C: quit S: +OK POP3 server signing off Problem 18 For a given input of domain name (such as ccn.com), IP address or network administrator name, the whois database can be used to locate the corresponding registrar, whois server, DNS server, and so on. NS4.YAHOO.COM from www.register.com; NS1.MSFT.NET from ww.register.com Local Domain: www.mindspring.com Web servers : www.mindspring.com 207.69.189.21, 207.69.189.22, 207.69.189.23, 207.69.189.24, 207.69.189.25, 207.69.189.26, 207.69.189.27, 207.69.189.28 Mail Servers : mx1.mindspring.com (207.69.189.217) mx2.mindspring.com (207.69.189.218) mx3.mindspring.com (207.69.189.219) mx4.mindspring.com (207.69.189.220) Name Servers: itchy.earthlink.net (207.69.188.196) scratchy.earthlink.net (207.69.188.197) www.yahoo.com Web Servers: www.yahoo.com (216.109.112.135, 66.94.234.13) Mail Servers: a.mx.mail.yahoo.com (209.191.118.103) b.mx.mail.yahoo.com (66.196.97.250) c.mx.mail.yahoo.com (68.142.237.182, 216.39.53.3) d.mx.mail.yahoo.com (216.39.53.2) e.mx.mail.yahoo.com (216.39.53.1) f.mx.mail.yahoo.com (209.191.88.247, 68.142.202.247) g.mx.mail.yahoo.com (209.191.88.239, 206.190.53.191) Name Servers: ns1.yahoo.com (66.218.71.63) ns2.yahoo.com (68.142.255.16) ns3.yahoo.com (217.12.4.104) ns4.yahoo.com (68.142.196.63) ns5.yahoo.com (216.109.116.17) ns8.yahoo.com (202.165.104.22) ns9.yahoo.com (202.160.176.146) www.hotmail.com Web Servers: www.hotmail.com (64.4.33.7, 64.4.32.7) Mail Servers: mx1.hotmail.com (65.54.245.8, 65.54.244.8, 65.54.244.136) mx2.hotmail.com (65.54.244.40, 65.54.244.168, 65.54.245.40) mx3.hotmail.com (65.54.244.72, 65.54.244.200, 65.54.245.72) mx4.hotmail.com (65.54.244.232, 65.54.245.104, 65.54.244.104) Name Servers: ns1.msft.net (207.68.160.190) ns2.msft.net (65.54.240.126) ns3.msft.net (213.199.161.77) ns4.msft.net (207.46.66.126) ns5.msft.net (65.55.238.126) d) The yahoo web server has multiple IP addresses www.yahoo.com (216.109.112.135, 66.94.234.13) e) The address range for Polytechnic University: 128.238.0.0 – 128.238.255.255 f) An attacker can use the whois database and nslookup tool to determine the IP address ranges, DNS server addresses, etc., for the target institution. By analyzing the source address of attack packets, the victim can use whois to obtain information about domain from which the attack is coming and possibly inform the administrators of the origin domain. Problem 19 The following delegation chain is used for gaia.cs.umass.edu a.root-servers.net E.GTLD-SERVERS.NET ns1.umass.edu(authoritative) First command: dig +norecurse @a.root-servers.net any gaia.cs.umass.edu ;; AUTHORITY SECTION: edu. 172800 IN NS E.GTLD-SERVERS.NET. edu. 172800 IN NS A.GTLD-SERVERS.NET. edu. 172800 IN NS G3.NSTLD.COM. edu. 172800 IN NS D.GTLD-SERVERS.NET. edu. 172800 IN NS H3.NSTLD.COM. edu. 172800 IN NS L3.NSTLD.COM. edu. 172800 IN NS M3.NSTLD.COM. edu. 172800 IN NS C.GTLD-SERVERS.NET. Among all returned edu DNS servers, we send a query to the first one. dig +norecurse @E.GTLD-SERVERS.NET any gaia.cs.umass.edu umass.edu. 172800 IN NS ns1.umass.edu. umass.edu. 172800 IN NS ns2.umass.edu. umass.edu. 172800 IN NS ns3.umass.edu. Among all three returned authoritative DNS servers, we send a query to the first one. dig +norecurse @ns1.umass.edu any gaia.cs.umass.edu gaia.cs.umass.edu. 21600 IN A 128.119.245.12 The answer for google.com could be: a.root-servers.net E.GTLD-SERVERS.NET ns1.google.com(authoritative) Problem 20 We can periodically take a snapshot of the DNS caches in the local DNS servers. The Web server that appears most frequently in the DNS caches is the most popular server. This is because if more users are interested in a Web server, then DNS requests for that server are more frequently sent by users. Thus, that Web server will appear in the DNS caches more frequently. For a complete measurement study, see: Craig E. Wills, Mikhail Mikhailov, Hao Shang “Inferring Relative Popularity of Internet Applications by Actively Querying DNS Caches”, in IMC'03, October 2729, 2003, Miami Beach, Florida, USA Problem 21 Yes, we can use dig to query that Web site in the local DNS server. For example, “dig cnn.com” will return the query time for finding cnn.com. If cnn.com was just accessed a couple of seconds ago, an entry for cnn.com is cached in the local DNS cache, so the query time is 0 msec. Otherwise, the query time is large. Problem 22 For calculating the minimum distribution time for client-server distribution, we use the following formula: Dcs = max {NF/us, F/dmin} Similarly, for calculating the minimum distribution time for P2P distribution, we use the following formula: Where, F = 15 Gbits = 15 * 1024 Mbits us = 30 Mbps dmin = di = 2 Mbps Note, 300Kbps = 300/1024 Mbps. Client Server N 10 100 1000 u 300 Kbps 7680 51200 512000 700 Kbps 7680 51200 512000 2 Mbps 7680 51200 512000 Peer to Peer N 10 100 1000 u 300 Kbps 7680 25904 47559 700 Kbps 7680 15616 21525 2 Mbps 7680 7680 7680 Problem 23 Consider a distribution scheme in which the server sends the file to each client, in parallel, at a rate of a rate of us/N. Note that this rate is less than each of the client’s download rate, since by assumption us/N ≤ dmin. Thus each client can also receive at rate us/N. Since each client receives at rate us/N, the time for each client to receive the entire file is F/( us/N) = NF/ us. Since all the clients receive the file in NF/ us, the overall distribution time is also NF/ us. Consider a distribution scheme in which the server sends the file to each client, in parallel, at a rate of dmin. Note that the aggregate rate, N dmin, is less than the server’s link rate us, since by assumption us/N ≥ dmin. Since each client receives at rate dmin, the time for each client to receive the entire file is F/ dmin. Since all the clients receive the file in this time, the overall distribution time is also F/ dmin. From Section 2.6 we know that DCS ≥ max {NF/us, F/dmin} (Equation 1) Suppose that us/N ≤ dmin. Then from Equation 1 we have DCS ≥ NF/us . But from (a) we have DCS ≤ NF/us . Combining these two gives: DCS = NF/us when us/N ≤ dmin. (Equation 2) We can similarly show that: DCS =F/dmin when us/N ≥ dmin (Equation 3). Combining Equation 2 and Equation 3 gives the desired result. Problem 24 Define u = u1 + u2 + ….. + uN. By assumption us <= (us + u)/N Equation 1 Divide the file into N parts, with the ith part having size (ui/u)F. The server transmits the ith part to peer i at rate ri = (ui/u)us. Note that r1 + r2 + ….. + rN = us, so that the aggregate server rate does not exceed the link rate of the server. Also have each peer i forward the bits it receives to each of the N-1 peers at rate ri. The aggregate forwarding rate by peer i is (N-1)ri. We have (N-1)ri = (N-1)(usui)/u = (us + u)/N Equation 2 Let ri = ui/(N-1) and rN+1 = (us – u/(N-1))/N In this distribution scheme, the file is broken into N+1 parts. The server sends bits from the ith part to the ith peer (i = 1, …., N) at rate ri. Each peer i forwards the bits arriving at rate ri to each of the other N-1 peers. Additionally, the server sends bits from the (N+1) st part at rate rN+1 to each of the N peers. The peers do not forward the bits from the (N+1)st part. The aggregate send rate of the server is r1+ …. + rN + N rN+1 = u/(N-1) + us – u/(N-1) = us Thus, the server’s send rate does not exceed its link rate. The aggregate send rate of peer i is (N-1)ri = ui Thus, each peer’s send rate does not exceed its link rate. In this distribution scheme, peer i receives bits at an aggregate rate of Thus each peer receives the file in NF/(us+u). (For simplicity, we neglected to specify the size of the file part for i = 1, …., N+1. We now provide that here. Let Δ = (us+u)/N be the distribution time. For i = 1, …, N, the ith file part is Fi = ri Δ bits. The (N+1)st file part is FN+1 = rN+1 Δ bits. It is straightforward to show that F1+ ….. + FN+1 = F.) The solution to this part is similar to that of 17 (c). We know from section 2.6 that Combining this with a) and b) gives the desired result. Problem 25 There are N nodes in the overlay network. There are N(N-1)/2 edges. Problem 26 Yes. His first claim is possible, as long as there are enough peers staying in the swarm for a long enough time. Bob can always receive data through optimistic unchoking by other peers. His second claim is also true. He can run a client on each host, let each client “free-ride,” and combine the collected chunks from the different hosts into a single file. He can even write a small scheduling program to make the different hosts ask for different chunks of the file. This is actually a kind of Sybil attack in P2P networks. Problem 27 Peer 3 learns that peer 5 has just left the system, so Peer 3 asks its first successor (Peer 4) for the identifier of its immediate successor (peer 8). Peer 3 will then make peer 8 its second successor. Problem 28 Peer 6 would first send peer 15 a message, saying “what will be peer 6’s predecessor and successor?” This message gets forwarded through the DHT until it reaches peer 5, who realizes that it will be 6’s predecessor and that its current successor, peer 8, will become 6’s successor. Next, peer 5 sends this predecessor and successor information back to 6. Peer 6 can now join the DHT by making peer 8 its successor and by notifying peer 5 that it should change its immediate successor to 6. Problem 29 For each key, we first calculate the distances (using d(k,p)) between itself and all peers, and then store the key in the peer that is closest to the key (that is, with smallest distance value). Problem 30 Yes, randomly assigning keys to peers does not consider the underlying network at all, so it very likely causes mismatches. Such mismatches may degrade the search performance. For example, consider a logical path p1 (consisting of only two logical links): ABC, where A and B are neighboring peers, and B and C are neighboring peers. Suppose that there is another logical path p2 from A to C (consisting of 3 logical links): ADEC. It might be the case that A and B are very far away physically (and separated by many routers), and B and C are very far away physically (and separated by many routers). But it may be the case that A, D, E, and C are all very close physically (and all separated by few routers). In other words, a shorter logical path may correspond to a much longer physical path. Problem 31 If you run TCPClient first, then the client will attempt to make a TCP connection with a non-existent server process. A TCP connection will not be made. UDPClient doesn't establish a TCP connection with the server. Thus, everything should work fine if you first run UDPClient, then run UDPServer, and then type some input into the keyboard. If you use different port numbers, then the client will attempt to establish a TCP connection with the wrong process or a non-existent process. Errors will occur. Problem 32 In the original program, UDPClient does not specify a port number when it creates the socket. In this case, the code lets the underlying operating system choose a port number. With the additional line, when UDPClient is executed, a UDP socket is created with port number 5432 . UDPServer needs to know the client port number so that it can send packets back to the correct client socket. Glancing at UDPServer, we see that the client port number is not “hard-wired” into the server code; instead, UDPServer determines the client port number by unraveling the datagram it receives from the client. Thus UDP server will work with any client port number, including 5432. UDPServer therefore does not need to be modified. Before: Client socket = x (chosen by OS) Server socket = 9876 After: Client socket = 5432 Problem 33 Yes, you can configure many browsers to open multiple simultaneous connections to a Web site. The advantage is that you will you potentially download the file faster. The disadvantage is that you may be hogging the bandwidth, thereby significantly slowing down the downloads of other users who are sharing the same physical links. Problem 34 For an application such as remote login (telnet and ssh), a byte-stream oriented protocol is very natural since there is no notion of message boundaries in the application. When a user types a character, we simply drop the character into the TCP connection. In other applications, we may be sending a series of messages that have inherent boundaries between them. For example, when one SMTP mail server sends another SMTP mail server several email messages back to back. Since TCP does not have a mechanism to indicate the boundaries, the application must add the indications itself, so that receiving side of the application can distinguish one message from the next. If each message were instead put into a distinct UDP segment, the receiving end would be able to distinguish the various messages without any indications added by the sending side of the application. Problem 35 To create a web server, we need to run web server software on a host. Many vendors sell web server software. However, the most popular web server software today is Apache, which is open source and free. Over the years it has been highly optimized by the open-source community. Problem 36 The key is the infohash, the value is an IP address that currently has the file designated by the infohash. Chapter 3 Review Questions Call this protocol Simple Transport Protocol (STP). At the sender side, STP accepts from the sending process a chunk of data not exceeding 1196 bytes, a destination host address, and a destination port number. STP adds a four-byte header to each chunk and puts the port number of the destination process in this header. STP then gives the destination host address and the resulting segment to the network layer. The network layer delivers the segment to STP at the destination host. STP then examines the port number in the segment, extracts the data from the segment, and passes the data to the process identified by the port number. The segment now has two header fields: a source port field and destination port field. At the sender side, STP accepts a chunk of data not exceeding 1192 bytes, a destination host address, a source port number, and a destination port number. STP creates a segment which contains the application data, source port number, and destination port number. It then gives the segment and the destination host address to the network layer. After receiving the segment, STP at the receiving host gives the application process the application data and the source port number. No, the transport layer does not have to do anything in the core; the transport layer “lives” in the end systems. For sending a letter, the family member is required to give the delegate the letter itself, the address of the destination house, and the name of the recipient. The delegate clearly writes the recipient’s name on the top of the letter. The delegate then puts the letter in an envelope and writes the address of the destination house on the envelope. The delegate then gives the letter to the planet’s mail service. At the receiving side, the delegate receives the letter from the mail service, takes the letter out of the envelope, and takes note of the recipient name written at the top of the letter. The delegate then gives the letter to the family member with this name. No, the mail service does not have to open the envelope; it only examines the address on the envelope. Source port number y and destination port number x. An application developer may not want its application to use TCP’s congestion control, which can throttle the application’s sending rate at times of congestion. Often, designers of IP telephony and IP videoconference applications choose to run their applications over UDP because they want to avoid TCP’s congestion control. Also, some applications do not need the reliable data transfer provided by TCP. Since most firewalls are configured to block UDP traffic, using TCP for video and voice traffic lets the traffic though the firewalls. Yes. The application developer can put reliable data transfer into the application layer protocol. This would require a significant amount of work and debugging, however. Yes, both segments will be directed to the same socket. For each received segment, at the socket interface, the operating system will provide the process with the IP addresses to determine the origins of the individual segments. For each persistent connection, the Web server creates a separate “connection socket”. Each connection socket is identified with a four-tuple: (source IP address, source port number, destination IP address, destination port number). When host C receives and IP datagram, it examines these four fields in the datagram/segment to determine to which socket it should pass the payload of the TCP segment. Thus, the requests from A and B pass through different sockets. The identifier for both of these sockets has 80 for the destination port; however, the identifiers for these sockets have different values for source IP addresses. Unlike UDP, when the transport layer passes a TCP segment’s payload to the application process, it does not specify the source IP address, as this is implicitly specified by the socket identifier. Sequence numbers are required for a receiver to find out whether an arriving packet contains new data or is a retransmission. To handle losses in the channel. If the ACK for a transmitted packet is not received within the duration of the timer for the packet, the packet (or its ACK or NACK) is assumed to have been lost. Hence, the packet is retransmitted. A timer would still be necessary in the protocol rdt 3.0. If the round trip time is known then the only advantage will be that, the sender knows for sure that either the packet or the ACK (or NACK) for the packet has been lost, as compared to the real scenario, where the ACK (or NACK) might still be on the way to the sender, after the timer expires. However, to detect the loss, for each packet, a timer of constant duration will still be necessary at the sender. The packet loss caused a time out after which all the five packets were retransmitted. Loss of an ACK didn’t trigger any retransmission as Go-Back-N uses cumulative acknowledgements. The sender was unable to send sixth packet as the send window size is fixed to 5. When the packet was lost, the received four packets were buffered the receiver. After the timeout, sender retransmitted the lost packet and receiver delivered the buffered packets to application in correct order. Duplicate ACK was sent by the receiver for the lost ACK. The sender was unable to send sixth packet as the send win

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Drag and Drop Component Suite Version 4.1 Field test 5, released 16-dec-2001 ?1997-2001 Angus Johnson & Anders Melander http://www.melander.dk/delphi/dragdrop/ ------------------------------------------- Table of Contents: ------------------------------------------- 1. Supported platforms 2. Installation 3. Getting started 4. Known problems 5. Support and feedback 6. Bug reports 7. Upgrades and bug fixes 8. Missing in this release 9. New in version 4.x 10. TODO 11. Licence, Copyright and Disclaimer 12. Release history ------------------------------------------- 1. Supported platforms: ------------------------------------------- This release supports Delphi 4-6 and C++ Builder 4-5. Earlier versions of Delphi and C++ Builder will not be supported. If you need Delphi 3 or C++ Builder 3 support you will have to revert to version 3.7 of the Drag and Drop Component Suite. The library has been tested on NT4 service pack 5 and Windows 2000. Windows 95, 98, ME and XP should be supported, but has not been tested. Linux and Kylix are not supported. There are *NO* plans to port the library to Kylix. The drag and drop protocols available on Linux are too much of a mess at this time. ------------------------------------------- 2. Installation: ------------------------------------------- 1) Before you do anything else, read the "Known problems" section of this document. 2) Install the source into a directory of your choice. The files are installed into three directories: DragDrop DragDrop\Components DragDrop\Demo 3) Install and compile the appropriate design time package. The design time packages are located in the Components directory. Each version of Delphi and C++ Builder has its own package; DragDropD6.dpk for Delphi 6, DragDropD5.dpk for Delphi 5, DragDropC5.bpk for C++ Builder 5, etc. 4) Add the Drag and Drop Component Suite components directory to your library path. 5) Load the demo project group: demo\dragdrop_delphi.bpg for Delphi 5 and 6 demo\dragdrop_bcb4.bpg for C++ Builder 4 demo\dragdrop_bcb5.bpg for C++ Builder 5 The project group contains all the demo applications. 6) If your version of Delphi does not support text format DFM files (e.g. Delphi 4 doesn't), you will have to use the convert.exe utility supplied with Delphi to convert all the demo form files to binary format. A batch file, convert_forms_to delphi_4_format.bat, is supplied in the demo directory which automates the conversion process. The C++ Builder demo forms are distributed in binary format. 7) If upgrading from a previous version of the Drag and Drop Component Suite, please read the document "upgrading_to_v4.txt" before you begin working on your existing projects. Note about "Property does not exist" errors: Since all demos were developed with the latest version of Delphi, most of the demo forms probably contains references to properties that doesn't exist in earlier versions of Delphi and C++ Builder. Because of this you will get fatal run-time errors (e.g. "Error reading blahblahblah: Property does not exist.") if you attemt to run the demos without fixing this problem. Luckily it is very easy to make the forms work again; Just open the forms in the IDE, then select "Ignore All" when the IDE complains that this or that property doesn't exist and finally save the forms. ------------------------------------------- 3. Getting started: ------------------------------------------- It is recommended that you start by running each of the demo applications and then look through the demo source. Each demo application is supplied with a readme.txt file which briefly describes what the demo does and what features it uses. The demos should be run in the order in which they are listed in the supplied project group. Even if you have used previous versions of the Drag and Drop Component Suite it would be a good idea to have a quick look at the demos. The library has been completely rewritten and a lot of new features has been added. ------------------------------------------- 4. Known problems: ------------------------------------------- * The Shell Extension components does not support C++ Builder 4. For some strange reason the components causes a link error. * There appear to be sporadic problems compiling with C++ Builder 5. Several user have reported that they occasionally get one or more of the following compiler errors: [C++ Error] DragDropFile.hpp(178): E2450 Undefined structure '_FILEDESCRIPTORW' [C++ Error] DropSource.hpp(135): E2076 Overloadable operator expected I have not been able to reproduce these errors, but I believe the following work around will fix the problem: In the project options of *all* projects which uses these components, add the following conditional define: NO_WIN32_LEAN_AND_MEAN The define *must* be made in the project options. It is not sufficient to #define it in the source. If you manage to compile with C++ Builder (any version), I would very much like to know about it. * Delphi's and C++ Builder's HWND and THandle types are not compatible. For this reason it might be nescessary to cast C++ Builder's HWND values to Delphi's THandle type when a HWND is passed to a function. E.g.: if (DragDetectPlus(THandle(MyControl->Handle), Point(X, Y))) { ... } * Virtual File Stream formats can only be pasted from the clipboard with live data (i.e. FlushClipboard/OleFlushClipboard hasn't been called on the data source). This problem affects TFileContentsStreamOnDemandClipboardFormat and the VirtualFileStream demo. This is believed to be a bug in the Windows clipboard and a work around hasn't been found yet. * Asynchronous targets appears to be broken in the current release. * When TDropFileTarget.GetDataOnEnter is set to True, the component doesn't work with WinZip. Although the file names are received correctly by TDropFileTarget, WinZip doesn't extract the files and the files thus can't be copied/moved. This is caused by a quirk in WinZip; Apparently WinZip doesn't like IDataObject.GetData to be called before IDropTarget.Drop is called. ------------------------------------------- 5. Support and feedback: ------------------------------------------- Since these components are freeware they are also unsupported. You are welcome to ask for help via email, but I cannot guarantee that I will have time to help you or even reply to your mail. If you absolytely can't live without my help, you can alway try bribing me. You can also try asking for help in the Delphi newsgroups. Since the Drag and Drop Component Suite is in widespread use, there's a good chance another user can help you. I recommend the following newsgroups for issues regarding this library (or COM based Drag/Drop in general): borland.public.delphi.winapi borland.public.delphi.thirdparty-tools borland.public.delphi.oleautomation borland.public.cppbuilder.winapi borland.public.cppbuilder.thirdparty-tools Please choose the most appropiate newsgroup for your question. Do not cross post to them all. Before posting to the newsgroups, I suggest you try to search for an answer on the Google (DejaNews) search engine: http://groups.google.com Chances are that your question has been asked and answered before. If you have suggestions for improvements please mail them to me: anders@melander.dk Please include the words "Drag Drop" in the subject of any email regarding these components. ------------------------------------------- 6. Bug reports: ------------------------------------------- Bugs can either be reported at my home page (http://www.melander.dk/) or mailed directly to me: anders@melander.dk. When reporting a bug, please provide the following information: * The exact version of the Drag and Drop Component Suite you are using. * The exact version of Delphi or C++ Builder you are using. * The name and exact version of your operating system (e.g. NT4 SP5). * The exact version of the Internet Explorer installed on your system. If you can provide me with a minimal application which reproduces the problem, I can almost guarantee that I will be able to fix the problem in very short time. Please supply only the source files (pas, dfm, dpr, dof, res, etc.) and mail them as a single zip file. If I need a compiled version I will ask for it. If you feel you need to send me a screen shot, please send it in GIF or PNG format. If you mail a bug report to me, please include the words "Drag Drop" in the subject of your email. ------------------------------------------- 7. Upgrades and bug fixes: ------------------------------------------- Upgrades can be downloaded from my home page: http://www.melander.dk/delphi/dragdrop/ Bug fixes will also be posted to the above page. If you have registered for update notification via the installation program, you will receive email notification when a new release is available. You will not be notified of bug fixes. You can use the installation program to check for and download new releases and to check for known bugs. Note: If a new release is made available and you are not notified even though you registered for notification, you probably mistyped your email address during installation; About 10% of all registrations supply an invalid email address. ------------------------------------------- 8. Missing in this release: ------------------------------------------- * On-line help has not been updated and included in the kit due to late changes in the Delphi 6 help system and lack of time. If time permits, I will update the help and include it in a future release. ------------------------------------------- 9. New in version 4.x: ------------------------------------------- * Completely redesigned and rewritten. Previous versions of the Drag and Drop Component Suite used a very monolithic design and flat class hierachy which made it a bit cumbersome to extend the existing components or implement new ones. Version 4 is a complete rewrite and redesign, but still maintains compatibility with previous versions. The new V4 design basically separates the library into three layers: 1) Clipboard format I/O. 2) Data format conversion and storage. 3) COM Drag/Drop implementation and VCL component interface. The clipboard format layer is responsible for reading and writing data in different formats to and from an IDataObject interface. For each different clipboard format version 4 implements a specialized class which knows exactly how to interpret the clipboard format. For example the CF_TEXT (plain text) clipboard format is handled by the TTextClipboardFormat class and the CF_FILE (file names) clipboard format is handled by the TFileClipboardFormat class. The data format layer is primarily used to render the different clipboard formats to and from native Delphi data types. For example the TTextDataFormat class represents all text based clipboard formats (e.g. TTextClipboardFormat) as a string while the TFileDataFormat class represents a list of file names (e.g. TFileClipboardFormat) as a string list. The conversion between different data- and clipboard formats is handled by the same Assign/AssignTo mechanism as the VCLs TPersistent employes. This makes it possible to extend existing data formats with support for new clipboard formats without modification to the existing classes. The drag/drop component layer has several tasks; It implements the actual COM drag/drop functionality (i.e. it implements the IDropSource, IDropTarget and IDataObject interfaces (along with several other related interfaces)), it surfaces the data provided by the data format layer as component properties and it handles the interaction between the whole drag/drop framework and the users code. The suite provides a multitude of different components. Most are specialized for different drag/drop tasks (e.g. the TDropFileTarget and TDropFilesSource components for drag/drop of files), but some are either more generic, handling multiple unrelated formats, or simply helper components which are used to extend the existing components or build new ones. * Support for Delphi 6. Version 4.0 was primarily developed on Delphi 6 and then ported back to previous versions of Delphi and C++ Builder. * Support for Windows 2000 inter application drag images. On Windows platforms which supports it, drag images are now displayed when dragging between applications. Currently only Windows 2000 supports this feature. On platforms which doesn't support the feature, drag images are only displayed whithin the source application. * Support for Windows 2000 asynchronous data transfers. Asynchronous data tranfers allows the drop source and targets to perform slow transfers or to transfer large amounts of data without blocking the user interface while the data is being transfered. For platforms other than Windows 2000, the new TDropSourceThread class can be used to provide similar (but more limited) asynchronous data transfer capabilities. * Support for optimized and non-optimized move. When performing drag-move operations, it is now possible to specify if the target (optimized move) or the source (non-optimized move) is responsible for deleting the source files. * Support for delete-on-paste. When data is cut to the clipboard, it is now possible to defer the deletion of the source data until the target actually pastes the data. The source is notified by an event when the target pastes the data. * Extended clipboard support. All formats and components (both source and target) now support clipboard operations (copy/cut/paste) and the VCL clipboard object. * Support for shell drop handlers. The new TDropHandler component can be used to write drop handler shell extensions. A drop handler is a shell extension which is executed when a user drags and drops one or more files on a file associated wth your application. * Support for shell drag drop handlers. The new TDragDropHandler component can be used to write drag drop handler shell extensions. A drag drop handler is a shell extension which can extend the popup menu which is displayed when a user drag and drops files with the right mouse button. * Support for shell context menu handlers. The new TDropContextMenu component can be used to write context menu handler shell extensions. A context menu handler is a shell extension which can extend the popup menu which is displayed when a user right-clicks a file in the shell. * Drop sources can receive data from drop targets. It is now possible for drop targets to write data back to the drop source. This is used to support optimized-move, delete-on-paste and inter application drag images. * Automatic re-registration of targets when the target window handle is recreated. In previous versions, target controls would loose their ability to accept drops when their window handles were recreated by the VCL (e.g. when changing the border style or docking a form). This is no longer a problem. * Support for run-time definition of custom data formats. You can now add support for new clipboard formats without custom components. * Support for design-time extension of existing source and target components. Using the new TDataFormatAdapter component it is now possible to mix and match data formats and source and target components at design time. E.g. the TDropFileTarget component can be extended with URL support. * It is now possible to completely customize the target auto-scroll feature. Auto scroling can now be completely customized via the OnDragEnter, OnDragOver, OnGetDropEffect and OnScroll events and the public NoScrollZone and published AutoScroll properties. * Multiple target controls per drop target component. In previous versions you had to use one drop target component per target control. With version 4, each drop target component can handle any number of target controls. * It is now possible to specify the target control at design time. A published Target property has been added to the drop target components. * Includes 20 components: - TDropFileSource and TDropFileTarget Used for drag and drop of files. Supports recycle bin and PIDLs. - TDropTextSource and TDropTextTarget Used for drag and drop of text. - TDropBMPSource and TDropBMPTarget Used for drag and drop of bitmaps. - TDropPIDLSource and TDropPIDLTarget Used for drag and drop of PIDLs in native format. - TDropURLSource and TDropURLTarget Used for drag and drop of internet shortcuts. - TDropDummyTarget Used to provide drag/drop cursor feedback for controls which aren't registered as drop targets. - TDropComboTarget (new) Swiss-army-knife target. Accepts text, files, bitmaps, meta files, URLs and file contents. - TDropMetaFileTarget (new) Target which can accept meta files and enhanced meta files. - TDropImageTarget (new) Target which can accept bitmaps, DIBs, meta files and enhanced meta files. - TDragDropHandler (new) Used to implement Drag Drop Handler shell extensions. - TDropHandler (new) Used to implement Shell Drop Handler shell extensions. - TDragDropContext (new) Used to implement Shell Context Menu Handler shell extensions. - TDataFormatAdapter (new) Extends the standard source and target components with support for extra data formats. An alternative to TDropComboTarget. - TDropEmptySource and TDropEmptyTarget (new) Target and source components which doesn't support any formats, but can be extended with TDataFormatAdapter components. * Supports 27 standard clipboard formats: Text formats: - CF_TEXT (plain text) - CF_UNICODETEXT (Unicode text) - CF_OEMTEXT (Text in the OEM characterset) - CF_LOCALE (Locale specification) - 'Rich Text Format' (RTF text) - 'CSV' (Tabular spreadsheet text) File formats: - CF_HDROP (list of file names) - CF_FILEGROUPDESCRIPTOR, CF_FILEGROUPDESCRIPTORW and CF_FILECONTENTS (list of files and their attributes and content). - 'Shell IDList Array' (PIDLs) - 'FileName' and 'FileNameW' (single filename, used for 16 bit compatibility). - 'FileNameMap' and 'FileNameMapW' (used to rename files, usually when dragging from the recycle bin) Image formats: - CF_BITMAP (Windows bitmap) - CF_DIB (Device Independant Bitmap) - CF_METAFILEPICT (Windows MetaFile) - CF_ENHMETAFILE (Enhanced Metafile) - CF_PALETTE (Bitmap palette) Internet formats: - 'UniformResourceLocator' and 'UniformResourceLocatorW' (Internet shortcut) - 'Netscape Bookmark' (Netscape bookmark/URL) - 'Netscape Image Format' (Netscape image/URL) - '+//ISBN 1-887687-00-9::versit::PDI//vCard' (V-Card) - 'HTML Format' (HTML text) - 'Internet Message (rfc822/rfc1522)' (E-mail message in RFC822 format) Misc. formats: - CF_PREFERREDDROPEFFECT and CF_PASTESUCCEEDED (mostly used by clipboard) - CF_PERFORMEDDROPEFFECT and CF_LOGICALPERFORMEDDROPEFFECT (mostly used for optimized-move) - 'InShellDragLoop' (used by Windows shell) - 'TargetCLSID' (Mostly used when dragging to recycle-bin) * New source events: - OnGetData: Fired when the target requests data. - OnSetData: Fired when the target writes data back to the source. - OnPaste: Fired when the target pastes data which the source has placed on the clipboard. - OnAfterDrop: Fired after the drag/drop operation has completed. * New target events: - OnScroll: Fires when the target component is about to perform auto-scroll on the target control. - OnAcceptFormat: Fires when the target component needs to determine if it will accept a given data format. Only surfaced in the TDropComboTarget component. * 8 new demo applications, 19 in total. ------------------------------------------- 10. TODO (may or may not be implemented): ------------------------------------------- * Async target demo (with and without IAsyncOperation support). * Scrap file demo. * Native Outlook message format. * Structured storage support (IStorage encapsulation). ------------------------------------------- 11. Licence, Copyright and Disclaimer: ------------------------------------------- The Drag and Drop Component Suite is Copyright ?1997-2001 Angus Johnson and Anders Melander. All rights reserved. The software is copyrighted as noted above. It may be freely copied, modified, and redistributed, provided that the copyright notice(s) is preserved on all copies. The Drag and Drop Component Suite is freeware and we would like it to remain so. This means that it may not be bundled with commercial libraries or sold as shareware. You are welcome to use it in commercial and shareware applications providing you do not charge for the functionality provided by the Drag and Drop Component Suite. There is no warranty or other guarantee of fitness for this software, it is provided solely "as is". You are welcome to use the source to make your own modified components, and such modified components may be distributed by you or others if you include credits to the original components, and do not charge anything for your modified components. ------------------------------------------- 12. Version 4 release history: ------------------------------------------- 16-dec-2001 * Ported to C++ Builder 4. * Released for test as v4.1 FT5. 12-dec-2001 * Fixed C++ Builder name clash between TDropComboTarget.GetMetaFile and the GetMetaFile #define in wingdi.h 1-dec-2001 * The IAsyncOperation interface is now also declared as IAsyncOperation2 and all references to IAsyncOperation has been replaced with IAsyncOperation2. This was done to work around a bug in C++ Builder. Thanks to Jonathan Arnold for all his help with getting the components to work with C++ Builder. Without Jonathan's help version 4.1 would prabably have shipped witout C++ Builder support and certainly without any C++ Builder demos. * Demo applications for C++ Builder. The C++ Builder demos were contributed by Jonathan Arnold. 27-nov-2001 * TCustomDropTarget.Droptypes property renamed to DropTypes (notice the case). Thanks to Krystian Brazulewicz for spotting this. 24-nov-2001 * The GetURLFromString function in the DragDropInternet unit has been made public due to user request. 21-nov-2001 * Modified MakeHTML function to comply with Microsoft's description of the CF_HTML clipboard format. * Added MakeTextFromHTML function to convert CF_HTML data to plain HTML. Provides the reverse functionality of MakeHTML. * Added HTML support to TTextDataFormat class and TDropTextSource and TDropTextTarget components. * Fixed C++ Builder 5 problem with IAsyncOperation. * Released for test as v4.1 FT4. 10-nov-2001 * Added NetscapeDemo demo application. Demonstrates how to receive messages dropped from Netscape. This demo was sponsored by ThoughtShare Communications Inc. * Released for test as v4.1 FT3. 23-oct-2001 * Conversion priority of TURLDataFormat has been changed to give the File Group Descritor formats priority over the Internet Shortcut format. This resolves a problem where dropping an URL on the desktop would cause the desktop to assume that an Active Desktop item was to be created instead of an Internet Shortcut. Thanks to Allen Martin for reporting this problem. By luck this modification also happens to work around a bug in Mozilla and Netscape 6; Mozilla incorrectly supplies the UniformResourceLocator clipboard format in unicode format instead of ANSI format. Thanks to Florian Kusche for reporting this problem. * Added support for TFileGroupDescritorWClipboardFormat to TURLDataFormat. * Added declaration of FD_PROGRESSUI to DragDropFormats. * Added TURLWClipboardFormat which implements the "UniformResourceLocatorW" (a.k.a. CFSTR_INETURLW) clipboard format. Basically a Unicode version of CFSTR_SHELLURL/CFSTR_INETURL. The TURLWClipboardFormat class isn't used anywhere yet but will probably be supported by TURLDataFormat (and thus TDropURLTarget/TDropURLSource) in a later release. * Added experimental Shell Drag Image support. This relies on undodumented shell32.dll functions and probably won't be fully support before v4.2 (if ever). See InitShellDragImage in DropSource.pas. Thanks to Jim Kueneman for bringning these functions to my attention. 13-oct-2001 * TCustomDropSource.Destroy and TCustomDropMultiSource.Destroy changed to call FlushClipboard instead of EmptyClipboard. This means that clipboard contents will be preserved when the source application/component is terminated. * Added clipboard support to VirtualFileStream demo. * Modified VirtualFileStream demo to work around clipboard quirk with IStream medium. * Modified TCustomSimpleClipboardFormat to disable TYMED_ISTORAGE support by default. At present TYMED_ISTORAGE is only supported for drop targets and enabling it by default in TCustomSimpleClipboardFormat.Create caused a lot of clipboard operations (e.g. copy/paste of text) to fail. Thanks to Michael J Marshall for bringing this problem to my attention. * Modified TCustomSimpleClipboardFormat to read from the the TYMED_ISTREAM medium in small (1Mb) chunks and via a global memory buffer. This has resultet in a huge performance gain (several orders of magnitude) when transferring large amounts of data via the TYMED_ISTREAM medium. 3-oct-2001 * Fixed bug in TCustomDropSource.SetImageIndex. Thanks to Maxim Abramovich for spotting this. * Added missing default property values to TCustomDropSource. Thanks to Maxim Abramovich for spotting this. * DragDrop.pas and DragDropContext.pas updated for Delphi 4. * Reimplemented utility to convert DFM form files from Delphi 5/6 test format to Delphi 4/5 binary format. * Improved unregistration of Shell Extensions. Shell extension now completely (and safely) remove their registry entries when unregistered. * Deprecated support for C++ Builder 3. * Released for test as v4.1 FT2. 25-sep-2001 * Rewritten ContextMenuHandlerShellExt demo. The demo is now actually a quite useful utility which can be used to register and unregister ActiveX controls, COM servers and type libraries. It includes the same functionality as Borland's TRegSvr utility. 20-sep-2001 * Added support for cascading menus, ownerdraw and menu bitmaps to TDropContextMenu component. * Modified TFileContentsStreamOnDemandClipboardFormat to handle invalid parameter value (FormatEtcIn.lindex) when data is copied to clipboard. This works around an apparent bug in the Windows clipboard. Thanks to Steve Moss for reporting this problem. * Modified TEnumFormatEtc class to not enumerate empty clipboard formats. Thanks to Steve Moss for this improvement. 1-sep-2001 * Introduced TCustomDropTarget.AutoRegister property. The AutoRegister property is used to control if drop target controls should be automatically unregistered and reregistered when their window handle is recreated by the VCL. If AutoRegister is True, which is the default, then automatic reregistration will be performed. This property was introduced because the hidden child control, which is used to monitor the drop target control's window handle, can have unwanted side effects on the drop target control (e.g. TToolBar). * Deprecated support for Delphi 3. 22-jun-2001 * Redesigned TTextDataFormat to handle RTF, Unicode, CSV and OEM text without conversion. Moved TTextDataFormat class to DragDropText unit. Added support for TLocaleClipboardFormat. * Surfaced new text formats as properties in TDropTextSource and TDropTextTarget. Previous versions of the Text source and target components represented all supported text formats via the Text property. In order to enable users to handle the different text formats independantly, the text source and target components now has individual properties for ANSI, OEM, Unicode and RTF text formats. The text target component can automatically synthesize some of the formats from the others (e.g. OEM text from ANSI text), but applications which previously relied on all formats being represented by the Text property will have to be modified to handle the new properties. * Added work around for problem where TToolBar as a drop target would display the invisible target proxy window. * Fixed wide string bug in WriteFilesToZeroList. Thanks to Werner Lehmann for spotting this. 15-jun-2001 * Added work-around for Outlook Express IDataObject.QueryGetData quirk. 3-jun-2001 * Ported to C++ Builder 4 and 5. * Added missing DragDropDesign.pas unit to design time packages. * First attempt at C++ Builder 3 port.... failed. * Improved handling of oversized File Group Descriptor data. * Added support for IStorage medium to TFileContentsStreamClipboardFormat. This allows the TDropComboTarget component to accept messages dropped from Microsoft Outlook. This work was sponsored by ThoughtShare Communications Inc. 23-may-2001 * Ported to Delphi 4. * First attempt at C++ Builder 5 port.... failed. 18-may-2001 * Released as version 4.0. Note: Version 4.0 was released exclusively on the Delphi 6 Companion CD. * ContextMenuDemo and DropHandlerDemo application has been partially rewritten and renamed. ContextMenuDemo is now named ContextMenuHandlerShellExt. DropHandlerDemo is now named DropHandlerShellExt. * TDropContextMenu component has been rewitten. The TDropContextMenu now implements a context menu handler shell extension. In previous releases it implemented a drag drop handler shell extension. * The DragDropHandler.pas unit which implements the TDropHandler component has been renamed to DropHandler.pas. * Added new TDragDropHandler component. The new component, which lives in the DragDropHandler unit, is used to implement drag drop handler shell extensions. * Added DragDropHandlerShellExt demo application. * Removed misc incomplete demos from kit. * Fixed minor problem in VirtualFileStream demo which caused drops from the VirtualFile demo not to transfer content correctly. 11-may-2001 * Converted all demo forms to text DFM format. This has been nescessary to maintain compatibility between all supported versions of Delphi. * Fixed a bug in GetPIDLsFromFilenames which caused drag-link of files (dtLink with TDropFileSource) not to work. * Added readme.txt files to some demo applications. * Added missing tlb and C++ Builder files to install kit. * Released as FT4. 6-may-2001 * Added missing dfm files to install kit. * Tested with Delphi 5. Fixed Delphi 5 compatibility error in main.dfm of DragDropDemo. * Removed misc compiler warnings. * The AsyncTransferTarget and OleObjectDemo demos were incomplete and has been removed from the kit for the V4.0 release. The demos will be included in a future release. * Released as FT3. 3-may-2001 * Added missing dpr and bpg files to install kit. * Updated readme.txt with regard to lack of C++ Builder demos. * Released as FT2. 29-apr-2001 * Cleaned up for release. * Released as FT1. 23-feb-2001 * Modified TCustomDropTarget.FindTarget to handle overlapping targets (e.g. different targets at the same position but on different pages of a page control or notebook). Thanks to Roger Moe for spotting this problem. 13-feb-2001 * Renamed AsyncTransfer2 demo to AsyncTransferSource. * Added AsyncTransferTarget demo. * Replaced TChart in AsyncTransfer2 demo with homegrown pie-chart-thing. * Modified all IStream based target formats to support incremental transfer. * URW533 problem has finally been fixed. The cause of the problem, which is a bug in Delphi, was found by Stefan Hoffmeister. * Fixed free notification for TDropContextmenu and TDataFormatAdapter. 27-dec-2000 * Moved TVirtualFileStreamDataFormat and TFileContentsStreamOnDemandClipboardFormat classes from VirtualFileStream demo to DragDropFormats unit. * Added TClipboardFormat.DataFormat and TClipboardFormats.DataFormat property. * Added TDropEmptySource and TDropEmptyTarget components. These are basically do-nothing components for use with TDataFormatAdapter. * Rewritten AsyncTransfer2 demo. The demo now uses TDropEmptySource, TDataFormatAdapter and TVirtualFileStreamDataFormat to transfer 10Mb of data with progress feedback. * Rewritten VirtualFileStream demo. The demo now uses TDropEmptySource, TDropEmptyTarget, TDataFormatAdapter and TVirtualFileStreamDataFormat. * Fixed memory leak in TVirtualFileStreamDataFormat. This leak only affected the old VirtualFileStream demo. * Added support for full File Descriptor attribute set to TVirtualFileStreamDataFormat. It is now possible to specify file attributes such as file size and last modified time in addition to the filename. I plan to add similar features to the other classes which uses FileDescriptors (e.g. TDropFileSource and TDropFileTarget). 21-dec-2000 * Ported to Delphi 4. * Added workaround for design bug in either Explorer or the clipboard. Explorer and the clipboard's requirements to the cursor position of an IStream object are incompatible. Explorer requires the cursor to be at the beginning of stream and the clipboard requires the cursor to be at the end of stream. 15-dec-2000 * Fixed URW533 problem. I'll leave the description of the workaround in here for now in case the problem resurfaces. 11-dec-2000 * Fixed bug in filename to PIDL conversion (GetPIDLsFromFilenames) which affected TDropFileTarget. Thanks to Poul Halgaard J鴕gensen for reporting this. 4-dec-2000 * Added THTMLDataFormat. * Fixed a a few small bugs which affected clipboard operations. * Added {$ALIGN ON} to dragdrop.inc. Apparently COM drag/drop requires some structures to be word alligned. This change fixes problems where some of the demos would suddenly stop working. * The URW533 problem has resurfaced. See the "Known problems" section below. 13-nov-2000 * TCopyPasteDataFormat has been renamed to TFeedbackDataFormat. * Added support for the Windows 2000 "TargetCLSID" format with the TTargetCLSIDClipboardFormat class and the TCustomDropSource.TargetCLSID property. * Added support for the "Logical Performed DropEffect" format with the TLogicalPerformedDropEffectClipboardFormat class. The class is used internally by TCustomDropSource. 30-oct-2000 * Added ContextMenu demo and TDropContextMenu component. Demonstrates how to customize the context menu which is displayed when a file is dragged with the right mouse button and dropped in the shell. * Added TCustomDataFormat.GetData. With the introduction of the GetData method, Data Format classes can now be used stand-alone to extract data from an IDataObject. 20-oct-2000 * Added VirtualFileStream demo. Demonstrates how to use the "File Contents" and "File Group Descritor" clipboard formats to drag and drop virtual files (files which doesn't exist physically) and transfer the data on-demand via a stream. 14-oct-2000 * Added special drop target registration of TCustomRichEdit controls. TCustomRichEdit needs special attention because it implements its own drop target handling which prevents it to work with these components. TCustomDropTarget now disables a rich edit control's built in drag/drop handling when the control is registered as a drop target. * Added work around for Windows bug where IDropTarget.DragOver is called regardless that the drop has been rejected in IDropTarget.DragEnter. 12-oct-2000 * Fixed bug that caused docking to interfere with drop targets. Thanks to G. Bradley MacDonald for bringing the problem to my attention. 30-sep-2000 * The DataFormats property has been made public in the TCustomDropMultiTarget class. * Added VirtualFile demo. Demonstrates how to use the TFileContentsClipboardFormat and TFileGroupDescritorClipboardFormat formats to drag and drop a virtual file (a file which doesn't exist physically). 28-sep-2000 * Improved drop source detection of optimized move. When an optimized move is performed by a drop target, the drop source's Execute method will now return drDropMove. Previously drCancel was returned. The OnAfterDrop event must still be used to determine if a move operation were optimized or not. * Modified TCustomDropTarget.GetPreferredDropEffect to get data from the current IDataObject instead of from the VCL global clipboard. 18-sep-2000 * Fixed bug in DropComboTarget caused by the 17-sep-2000 TStreams modification. 17-sep-2000 * Added AsyncTransfer2 demo to demonstrate use of TDropSourceThread. * Renamed TStreams class to TStreamList. 29-aug-2000 * Added TDropSourceThread. TDropSourceThread is an alternative to Windows 2000 asynchronous data transfers but also works on other platforms than Windows 2000. TDropSourceThread is based on code contributed by E. J. Molendijk. 24-aug-2000 * Added support for Windows 2000 asynchronous data transfers. Added IAsyncOperation implementation to TCustomDropSource. Added TCustomDropSource.AllowAsyncTransfer and AsyncTransfer properties. 5-aug-2000 * Added work around for URW533 compiler bug. * Fixed D4 and D5 packages and updated a few demos. Obsolete DropMultiTarget were still referenced a few places. * Documented work around for C++ Builder 5 compiler error. See the Known Problems section later in this document for more information. 2-aug-2000 * The package files provided in the kit is now design-time only packages. In previous versions, the packages could be used both at design- and run-time. The change was nescessary because the package now contains design-time code. * Added possible work around for suspected C++ Builder bug. The bug manifests itself as a "Overloadable operator expected" compile time error. See the "Known problems" section of this document. * Rewrote CustomFormat1 demo. * Added CustomFormat2 demo. * TDataDirection members has been renamed from ddGet and ddSet to ddRead and ddWrite. * All File Group Descritor and File Contents clipboard formats has been moved from the DragDropFile unit to the DragDropFormats unit. * File Contents support has been added to TTextDataFormat. The support is currently only enabled for drop sources. * Renamed TDropMultiTarget component to TDropComboTarget. Note: This will break applications which uses the TDropMultiTarget component. You can use the following technique to port application from previous releases: 1) Install the new components. 2) Repeat step 3-8 for all units which uses the TDropMultiTarget component. 3) Make a backup of the unit (both pas and dfm file) just in case... 4) Open the unit in the IDE. 5) In the .pas file, replace all occurances of "TDropMultiTarget" with "TDropComboTarget". 6) View the form as text. 7) Replace all occurances of "TDropMultiTarget" with "TDropComboTarget". 8) Save the unit. * Renamed a lot of demo files and directories. * Added work around for yet another bug in TStreamAdapter. * Added TCustomStringClipboardFormat as new base class for TCustomTextClipboardFormat. This changes the class hierachy a bit for classes which previously descended from TCustomTextClipboardFormat: All formats which needs zero termination now descend from TCustomTextClipboardFormat and the rest descend from TCustomStringClipboardFormat. Added TrimZeroes property. Fixed zero termination bug in TCustomTextClipboardFormat and generally improved handling of zero terminated strings. Disabled zero trim in TCustomStringClipboardFormat and enabled it in TCustomTextClipboardFormat. 23-jul-2000 * Improved handling of long file names in DropHandler demo. Added work around for ParamStr bug. * Added TDataFormatAdapter component and adapter demo. TDataFormatAdapter is used to extend the existing source and target components with additional data format support without modifying them. It can be considered an dynamic alternative to the current TDropMultiTarget component. 17-jul-2000 * TDropHandler component and DropHandler demo fully functional. 14-jul-2000 * Tested with C++ Builder 5. * Fixed sporadic integer overflow bug in DragDetectPlus function. * Added shell drop handler support with TDropHandler component. This is a work in progress and is not yet functional. 1-jul-2000 * Tested with Delphi 4. * Support for Windows 2000 inter application drag images. * TRawClipboardFormat and TRawDataFormat classes for support of arbitrary unknown clipboard formats. The classes are used internally in the TCustomDropSource.SetData method to support W2K drag images.

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