How can i resolve it and generate a web service?

miaomiaoga 2002-03-12 01:40:22

(sorry,i can't used chinese now)

i tried to use the service sample(all generated by .NET web service
wizard)...like the follow:

[WebMethod]
public string HelloWorld()
{
return "Hello World";
}

but when i type the follow command to test the .NET service:
http://localhost/WebService1/Service1.asmx?WSDL

it shows error, and the error message at the follow:

Server Application Unavailable
The web application you are attempting to access on this web server is
currently unavailable. Please hit the "Refresh" button in your web browser
to retry your request.

Administrator Note: An error message detailing the cause of this specific
request failure can be found in the system event log of the web server.
Please review this log entry to discover what caused this error to occur.

and when i checked the event viewer,it shows two error message:

1->>aspnet_wp.exe could not be started. HRESULT for the failure: 80004005

2->>aspnet_wp.exe could not be launched because the username and/or password
supplied in the processModel section of the config file are invalid.

how about your suggestion? how can i resolve it?~~~hope you can help me..:)

--
Benny Ng

Benny_Wufree@hotmail.com

...全文

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miaomiaoga 2002-03-20

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嗯！行~~~加分！

miaomiaoga 2002-03-16

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惨。。。没人来理我。。。唉。。。

qqchen79 2002-03-16

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你生成过WebService的代理了吗？VS.NET里就是加Web Reference。
会有一个mywebservice1.dll之类的东西，把它和你的VB.NET程序(*.exe）放在一个目录下才行。

把username改成SYSTEM可不是什么好主意，安全上不太好。:)
但至少将就能用了。

miaomiaoga 2002-03-13

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Machine.config文件如下：
userName="machine" password="AutoGenerate"

webservice的目錄已經有讀和寫的權限了~~~還是不行。。。

USERNAME是不是要改為另外一些東西？

miaomiaoga 2002-03-13

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改成SYSTEM就行了。。。但我用一個VB。NET程序調用它的時候。。。出現以下信息：
An unhandled exception of type 'System.IO.FileNotFoundException' occurred in system.windows.forms.dll

Additional information: File or assembly name mywebservice1, or one of its dependencies, was not found.

是什麼意思？我無法運行下去。。

qqchen79 2002-03-12

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1. 看看你的Machine.config文件（再.net framework目录下）中的processModel::username是否存在？是什么值？
2. 你的WebService目录是否有读/执行权限？

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

1：外文原文 Struts——an open-source MVC implementation This article introduces Struts, a Model-View-Controller implementation that uses servlets and JavaServer Pages (JSP) technology. Struts can help you control change in your Web project and promote specialization. Even if you never implement a system with Struts, you may get some ideas for your future servlets and JSP page implementation. Introduction Kids in grade school put HTML pages on the Internet. However, there is a monumental difference between a grade school page and a professionally developed Web site. The page designer (or HTML developer) must understand colors, the customer, product flow, page layout, browser compatibility, image creation, JavaScript, and more. Putting a great looking site together takes a lot of work, and most Java developers are more interested in creating a great looking object interface than a user interface. JavaServer Pages (JSP) technology provides the glue between the page designer and the Java developer. If you have worked on a large-scale Web application, you understand the term change. Model-View-Controller (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data. Struts is an MVC implementation that uses Servlets 2.2 and JSP 1.1 tags, from the J2EE specifications, as part of the implementation. You may never implement a system with Struts, but looking at Struts may give you some ideas on your future Servlets and JSP implementations. Model-View-Controller (MVC) JSP tags solved only part of our problem. We still have issues with validation, flow control, and updating the state of the application. This is where MVC comes to the rescue. MVC helps resolve some of the issues with the single module approach by dividing the problem into three categories: • Model The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller. • View The view provides the presentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur. • Controller The controller reacts to the user input. It creates and sets the model. MVC Model 2 The Web brought some unique challenges to software developers, most notably the stateless connection between the client and the server. This stateless behavior made it difficult for the model to notify the view of changes. On the Web, the browser has to re-query the server to discover modification to the state of the application. Another noticeable change is that the view uses different technology for implementation than the model or controller. Of course, we could use Java (or PERL, C/C++ or what ever) code to generate HTML. There are several disadvantages to that approach: • Java programmers should develop services, not HTML. • Changes to layout would require changes to code. • Customers of the service should be able to create pages to meet their specific needs. • The page designer isn't able to have direct involvement in page development. • HTML embedded into code is ugly. For the Web, the classical form of MVC needed to change. Figure 4 displays the Web adaptation of MVC, also commonly known as MVC Model 2 or MVC 2. The ActionServlet class Do you remember the days of function mappings? You would map some input event to a pointer to a function. If you where slick, you would place the configuration information into a file and load the file at run time. Function pointer arrays were the good old days of structured programming in C. Life is better now that we have Java technology, XML, J2EE, and all that. The Struts Controller is a servlet that maps events (an event generally being an HTTP post) to classes. And guess what -- the Controller uses a configuration file so you don_t have to hard-code the values. Life changes, but stays the same. ActionServlet is the Command part of the MVC implementation and is the core of the Framework. ActionServlet (Command) creates and uses Action, an ActionForm, and ActionForward. As mentioned earlier, the struts-config.xml file configures the Command. During the creation of the Web project, Action and ActionForm are extended to solve the specific problem space. The file struts-config.xml instructs ActionServlet on how to use the extended classes. There are several advantages to this approach: • The entire logical flow of the application is in a hierarchical text file. This makes it easier to view and understand, especially with large applications. • The page designer does not have to wade through Java code to understand the flow of the application. • The Java developer does not need to recompile code when making flow changes. Command functionality can be added by extending ActionServlet. The ActionForm class ActionForm maintains the session state for the Web application. ActionForm is an abstract class that is sub-classed for each input form model. When I say input form model, I am saying ActionForm represents a general concept of data that is set or updated by a HTML form. For instance, you may have a UserActionForm that is set by an HTML Form. The Struts framework will: • Check to see if a UserActionForm exists; if not, it will create an instance of the class. • Struts will set the state of the UserActionForm using corresponding fields from the HttpServletRequest. No more dreadful request.getParameter() calls. For instance, the Struts framework will take fname from request stream and call UserActionForm.setFname(). • The Struts framework updates the state of the UserActionForm before passing it to the business wrapper UserAction. • Before passing it to the Action class, Struts will also conduct form state validation by calling the validation() method on UserActionForm. Note: This is not always wise to do. There might be ways of using UserActionForm in other pages or business objects, where the validation might be different. Validation of the state might be better in the UserAction class. • The UserActionForm can be maintained at a session level. Notes: • The struts-config.xml file controls which HTML form request maps to which ActionForm. • Multiple requests can be mapped UserActionForm. • UserActionForm can be mapped over multiple pages for things such as wizards. The Action class The Action class is a wrapper around the business logic. The purpose of Action class is to translate the HttpServletRequest to the business logic. To use Action, subclass and overwrite the process() method. The ActionServlet (Command) passes the parameterized classes to ActionForm using the perform() method. Again, no more dreadful request.getParameter() calls. By the time the event gets here, the input form data (or HTML form data) has already been translated out of the request stream and into an ActionForm class. Struts, an MVC 2 implementation Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design. This definition implies that Struts is a framework, rather than a library, but Struts also contains an extensive tag library and utility classes that work independently of the framework. Figure 5 displays an overview of Struts. Struts overview • Client browser An HTTP request from the client browser creates an event. The Web container will respond with an HTTP response. • Controller The Controller receives the request from the browser, and makes the decision where to send the request. With Struts, the Controller is a command design pattern implemented as a servlet. The struts-config.xml file configures the Controller. • Business logic The business logic updates the state of the model and helps control the flow of the application. With Struts this is done with an Action class as a thin wrapper to the actual business logic. • Model state The model represents the state of the application. The business objects update the application state. ActionForm bean represents the Model state at a session or request level, and not at a persistent level. The JSP file reads information from the ActionForm bean using JSP tags. • View The view is simply a JSP file. There is no flow logic, no business logic, and no model information -- just tags. Tags are one of the things that make Struts unique compared to other frameworks like Velocity. Note: "Think thin" when extending the Action class. The Action class should control the flow and not the logic of the application. By placing the business logic in a separate package or EJB, we allow flexibility and reuse. Another way of thinking about Action class is as the Adapter design pattern. The purpose of the Action is to "Convert the interface of a class into another interface the clients expect. Adapter lets classes work together that couldn_t otherwise because of incompatibility interface" (from Design Patterns - Elements of Reusable OO Software by Gof). The client in this instance is the ActionServlet that knows nothing about our specific business class interface. Therefore, Struts provides a business interface it does understand, Action. By extending the Action, we make our business interface compatible with Struts business interface. (An interesting observation is that Action is a class and not an interface. Action started as an interface and changed into a class over time. Nothing's perfect.) The Error classes The UML diagram also included ActionError and ActionErrors. ActionError encapsulates an individual error message. ActionErrors is a container of ActionError classes that the View can access using tags. ActionErrors is Struts way of keeping up with a list of errors. The ActionMapping class An incoming event is normally in the form of an HTTP request, which the servlet Container turns into an HttpServletRequest. The Controller looks at the incoming event and dispatches the request to an Action class. The struts-config.xml determines what Action class the Controller calls. The struts-config.xml configuration information is translated into a set of ActionMapping, which are put into container of ActionMappings. (If you have not noticed it, classes that end with s are containers) The ActionMapping contains the knowledge of how a specific event maps to specific Actions. The ActionServlet (Command) passes the ActionMapping to the Action class via the perform() method. This allows Action to access the information to control flow. ActionMappings ActionMappings is a collection of ActionMapping objects. Struts pros • Use of JSP tag mechanism The tag feature promotes reusable code and abstracts Java code from the JSP file. This feature allows nice integration into JSP-based development tools that allow authoring with tags. • Tag library Why re-invent the wheel, or a tag library? If you cannot find something you need in the library, contribute. In addition, Struts provides a starting point if you are learning JSP tag technology. • Open source You have all the advantages of open source, such as being able to see the code and having everyone else using the library reviewing the code. Many eyes make for great code review. • Sample MVC implementation Struts offers some insight if you want to create your own MVC implementation. • Manage the problem space Divide and conquer is a nice way of solving the problem and making the problem manageable. Of course, the sword cuts both ways. The problem is more complex and needs more management. Struts cons • Youth Struts development is still in preliminary form. They are working toward releasing a version 1.0, but as with any 1.0 version, it does not provide all the bells and whistles. • Change The framework is undergoing a rapid amount of change. A great deal of change has occurred between Struts 0.5 and 1.0. You may want to download the most current Struts nightly distributions, to avoid deprecated methods. In the last 6 months, I have seen the Struts library grow from 90K to over 270K. I had to modify my examples several times because of changes in Struts, and I am not going to guarantee my examples will work with the version of Struts you download. • Correct level of abstraction Does Struts provide the correct level of abstraction? What is the proper level of abstraction for the page designer? That is the $64K question. Should we allow a page designer access to Java code in page development? Some frameworks like Velocity say no, and provide yet another language to learn for Web development. There is some validity to limiting Java code access in UI development. Most importantly, give a page designer a little bit of Java, and he will use a lot of Java. I saw this happen all the time in Microsoft ASP development. In ASP development, you were supposed to create COM objects and then write a little ASP script to glue it all together. Instead, the ASP developers would go crazy with ASP script. I would hear "Why wait for a COM developer to create it when I can program it directly with VBScript?" Struts helps limit the amount of Java code required in a JSP file via tag libraries. One such library is the Logic Tag, which manages conditional generation of output, but this does not prevent the UI developer from going nuts with Java code. Whatever type of framework you decide to use, you should understand the environment in which you are deploying and maintaining the framework. Of course, this task is easier said than done. • Limited scope Struts is a Web-based MVC solution that is meant be implemented with HTML, JSP files, and servlets. • J2EE application support Struts requires a servlet container that supports JSP 1.1 and Servlet 2.2 specifications. This alone will not solve all your install issues, unless you are using Tomcat 3.2. I have had a great deal of problems installing the library with Netscape iPlanet 6.0, which is supposedly the first J2EE-compliant application server. I recommend visiting the Struts User Mailing List archive (see Resources) when you run into problems. • Complexity Separating the problem into parts introduces complexity. There is no question that some education will have to go on to understand Struts. With the constant changes occurring, this can be frustrating at times. Welcome to the Web. • Where is... I could point out other issues, for instance, where are the client side validations, adaptable workflow, and dynamic strategy pattern for the controller? However, at this point, it is too easy to be a critic, and some of the issues are insignificant, or are reasonable for a 1.0 release. The way the Struts team goes at it, Struts might have these features by the time you read this article, or soon after. Future of Struts Things change rapidly in this new age of software development. In less than 5 years, I have seen things go from cgi/perl, to ISAPI/NSAPI, to ASP with VB, and now Java and J2EE. Sun is working hard to adapt changes to the JSP/servlet architecture, just as they have in the past with the Java language and API. You can obtain drafts of the new JSP 1.2 and Servlet 2.3 specifications from the Sun Web site. Additionally, a standard tag library for JSP files is appearing. 2:外文资料翻译译文 Struts——MVC 的一种开放源码实现本文介绍 Struts，它是使用 servlet 和 JavaServer Pages 技术的一种 Model-View-Controller 实现。Struts 可帮助您控制 Web 项目中的变化并提高专业化水平。尽管您可能永远不会用 Struts 实现一个系统，但您可以将其中的一些思想用于您以后的 servlet 和 JSP 网页的实现中。简介小学生也可以在因特网上发布 HTML 网页。但是，小学生的网页和专业开发的网站有质的区别。网页设计人员（或者 HTML 开发人员）必须理解颜色、用户、生产流程、网页布局、浏览器兼容性、图像创建和 JavaScript 等等。设计漂亮的网站需要做大量的工作，大多数 Java 开发人员更注重创建优美的对象接口，而不是用户界面。JavaServer Pages (JSP) 技术为网页设计人员和 Java 开发人员提供了一种联系钮带。如果您开发过大型 Web 应用程序，您就理解变化这个词的含义。“模型-视图-控制器”(MVC) 就是用来帮助您控制变化的一种设计模式。MVC 减弱了业务逻辑接口和数据接口之间的耦合。Struts 是一种 MVC 实现，它将 Servlet 2.2 和 JSP 1.1 标记（属于 J2EE 规范）用作实现的一部分。尽管您可能永远不会用 Struts 实现一个系统，但了解一下 Struts 或许使您能将其中的一些思想用于您以后的 Servlet 的 JSP 实现中。模型-视图-控制器 (MVC) JSP 标记只解决了部分问题。我们还得处理验证、流程控制和更新应用程序的状态等问题。这正是 MVC 发挥作用的地方。MVC 通过将问题分为三个类别来帮助解决单一模块方法所遇到的某些问题： • Model（模型）模型包含应用程序的核心功能。模型封装了应用程序的状态。有时它包含的唯一功能就是状态。它对视图或控制器一无所知。 • View（视图）视图提供模型的表示。它是应用程序的外观。视图可以访问模型的读方法，但不能访问写方法。此外，它对控制器一无所知。当更改模型时，视图应得到通知。 • Controller（控制器）控制器对用户的输入作出反应。它创建并设置模型。 MVC Model 2 Web 向软件开发人员提出了一些特有的挑战，最明显的就是客户机和服务器的无状态连接。这种无状态行为使得模型很难将更改通知视图。在 Web 上，为了发现对应用程序状态的修改，浏览器必须重新查询服务器。另一个重大变化是实现视图所用的技术与实现模型或控制器的技术不同。当然，我们可以使用 Java（或者 PERL、C/C++ 或别的语言）代码生成 HTML。这种方法有几个缺点： • Java 程序员应该开发服务，而不是 HTML。 • 更改布局时需要更改代码。 • 服务的用户应该能够创建网页来满足它们的特定需要。 • 网页设计人员不能直接参与网页开发。 • 嵌在代码中的 HTML 很难看。对于 Web，需要修改标准的 MVC 形式。图 4 显示了 MVC 的 Web 改写版，通常也称为 MVC Model 2 或 MVC 2。 Struts，MVC 2 的一种实现 Struts 是一组相互协作的类、servlet 和 JSP 标记，它们组成一个可重用的 MVC 2 设计。这个定义表示 Struts 是一个框架，而不是一个库，但 Struts 也包含了丰富的标记库和独立于该框架工作的实用程序类。图 5 显示了 Struts 的一个概览。 Struts 概览 • Client browser（客户浏览器）来自客户浏览器的每个 HTTP 请求创建一个事件。Web 容器将用一个 HTTP 响应作出响应。 • Controller（控制器）控制器接收来自浏览器的请求，并决定将这个请求发往何处。就 Struts 而言，控制器是以 servlet 实现的一个命令设计模式。 struts-config.xml 文件配置控制器。 • 业务逻辑业务逻辑更新模型的状态，并帮助控制应用程序的流程。就 Struts 而言，这是通过作为实际业务逻辑“瘦”包装的 Action 类完成的。 • Model（模型）的状态模型表示应用程序的状态。业务对象更新应用程序的状态。ActionForm bean 在会话级或请求级表示模型的状态，而不是在持久级。JSP 文件使用 JSP 标记读取来自 ActionForm bean 的信息。 • View（视图）视图就是一个 JSP 文件。其中没有流程逻辑，没有业务逻辑，也没有模型信息 -- 只有标记。标记是使 Struts 有别于其他框架（如 Velocity）的因素之一。详细分析 Struts 图 6 显示的是 org.apache.struts.action 包的一个最简 UML 图。图 6 显示了 ActionServlet (Controller)、 ActionForm (Form State) 和 Action (Model Wrapper) 之间的最简关系。 ActionServlet 类您还记得函数映射的日子吗？在那时，您会将某些输入事件映射到一个函数指针上。如果您对此比较熟悉，您会将配置信息放入一个文件，并在运行时加载这个文件。函数指针数组曾经是用 C 语言进行结构化编程的很好方法。现在好多了，我们有了 Java 技术、XML、J2EE，等等。Struts 的控制器是将事件（事件通常是 HTTP post）映射到类的一个 servlet。正如您所料 -- 控制器使用配置文件以使您不必对这些值进行硬编码。时代变了，但方法依旧。 ActionServlet 是该 MVC 实现的 Command 部分，它是这一框架的核心。 ActionServlet (Command) 创建并使用 Action 、 ActionForm 和 ActionForward 。如前所述， struts-config.xml 文件配置该 Command。在创建 Web 项目时，您将扩展 Action 和 ActionForm 来解决特定的问题。文件 struts-config.xml 指示 ActionServlet 如何使用这些扩展的类。这种方法有几个优点： • 应用程序的整个逻辑流程都存储在一个分层的文本文件中。这使得人们更容易查看和理解它，尤其是对于大型应用程序而言。 • 网页设计人员不必费力地阅读 Java 代码来理解应用程序的流程。 • Java 开发人员也不必在更改流程以后重新编译代码。可以通过扩展 ActionServlet 来添加 Command 功能。 ActionForm 类 ActionForm 维护 Web 应用程序的会话状态。 ActionForm 是一个抽象类，必须为每个输入表单模型创建该类的子类。当我说输入表单模型时,是指 ActionForm 表示的是由 HTML 表单设置或更新的一般意义上的数据。例如，您可能有一个由 HTML 表单设置的 UserActionForm 。Struts 框架将执行以下操作： • 检查 UserActionForm 是否存在；如果不存在，它将创建该类的一个实例。 • Struts 将使用 HttpServletRequest 中相应的域设置 UserActionForm 的状态。没有太多讨厌的 request.getParameter() 调用。例如，Struts 框架将从请求流中提取 fname ，并调用 UserActionForm.setFname() 。 • Struts 框架在将 UserActionForm 传递给业务包装 UserAction 之前将更新它的状态。 • 在将它传递给 Action 类之前，Struts 还会对 UserActionForm 调用 validation() 方法进行表单状态验证。注：这并不总是明智之举。别的网页或业务可能使用 UserActionForm ，在这些地方，验证可能有所不同。在 UserAction 类中进行状态验证可能更好。 • 可在会话级维护 UserActionForm 。注： • struts-config.xml 文件控制 HTML 表单请求与 ActionForm 之间的映射关系。 • 可将多个请求映射到 UserActionForm 。 • UserActionForm 可跨多页进行映射，以执行诸如向导之类的操作。 Action 类 Action 类是业务逻辑的一个包装。 Action 类的用途是将 HttpServletRequest 转换为业务逻辑。要使用 Action ，请创建它的子类并覆盖 process() 方法。 ActionServlet (Command) 使用 perform() 方法将参数化的类传递给 ActionForm 。仍然没有太多讨厌的 request.getParameter() 调用。当事件进展到这一步时，输入表单数据（或 HTML 表单数据）已被从请求流中提取出来并转移到 ActionForm 类中。注：扩展 Action 类时请注意简洁。 Action 类应该控制应用程序的流程，而不应该控制应用程序的逻辑。通过将业务逻辑放在单独的包或 EJB 中，我们就可以提供更大的灵活性和可重用性。考虑 Action 类的另一种方式是 Adapter 设计模式。 Action 的用途是“将类的接口转换为客户机所需的另一个接口。Adapter 使类能够协同工作，如果没有 Adapter，则这些类会因为不兼容的接口而无法协同工作。”（摘自 Gof 所著的 Design Patterns - Elements of Reusable OO Software ）。本例中的客户机是 ActionServlet ，它对我们的具体业务类接口一无所知。因此，Struts 提供了它能够理解的一个业务接口，即 Action 。通过扩展 Action ，我们使得我们的业务接口与 Struts 业务接口保持兼容。（一个有趣的发现是， Action 是类而不是接口）。 Action 开始为一个接口，后来却变成了一个类。真是金无足赤。） ActionMapping 类输入事件通常是在 HTTP 请求表单中发生的，servlet 容器将 HTTP 请求转换为 HttpServletRequest 。控制器查看输入事件并将请求分派给某个 Action 类。 struts-config.xml 确定 Controller 调用哪个 Action 类。 struts-config.xml 配置信息被转换为一组 ActionMapping ，而后者又被放入 ActionMappings 容器中。（您可能尚未注意到这一点，以 s结尾的类就是容器） ActionMapping 包含有关特定事件如何映射到特定 Action 的信息。 ActionServlet (Command) 通过 perform() 方法将 ActionMapping 传递给 Action 类。这样就使 Action 可访问用于控制流程的信息。 ActionMappings ActionMappings 是 ActionMapping 对象的一个集合。 Struts 的优点 • JSP 标记机制的使用标记特性从 JSP 文件获得可重用代码和抽象 Java 代码。这个特性能很好地集成到基于 JSP 的开发工具中，这些工具允许用标记编写代码。 • 标记库为什么要另发明一种轮子，或标记库呢？如果您在库中找不到您所要的标记，那就自己定义吧。此外，如果您正在学习 JSP 标记技术，则 Struts 为您提供了一个起点。 • 开放源码您可以获得开放源码的全部优点，比如可以查看代码并让使用库的每个人检查代码。许多人都可以进行很好的代码检查。 • MVC 实现样例如果您希望创建您自己的 MVC 实现，则 Struts 可增加您的见识。 • 管理问题空间分治是解决问题并使问题可管理的极好方法。当然，这是一把双刃剑。问题越来越复杂，并且需要越来越多的管理。 Struts 的缺点 • 仍处于发展初期 Struts 开发仍处于初级阶段。他们正在向着发行版本 1.0 而努力，但与任何 1.0 版本一样，它不可能尽善尽美。 • 仍在变化中这个框架仍在快速变化。Struts 1.0 与 Struts 0.5 相比变化极大。为了避免使用不赞成使用的方法，您可能隔一天就需要下载最新的 Struts。在过去的 6 个月中，我目睹 Struts 库从 90K 增大到 270K 以上。由于 Struts 中的变化，我不得不数次修改我的示例，但我不保证我的示例能与您下载的 Struts 协同工作。 • 正确的抽象级别 Struts 是否提供了正确的抽象级别？对于网页设计人员而言，什么是正确的抽象级别呢？这是一个用 $64K 的文字才能解释清楚的问题。在开发网页的过程中，我们是否应该让网页设计人员访问 Java 代码？某些框架（如 Velocity）说不应该，但它提供了另一种 Web 开发语言让我们学习。在 UI 开发中限制访问 Java 有一定的合理性。最重要的是，如果让网页设计人员使用一点 Java，他将使用大量的 Java。在 Microsoft ASP 的开发中，我总是看到这样的情况。在 ASP 开发中，您应该创建 COM 对象，然后编写少量的 ASP 脚本将这些 COM 对象联系起来。但是，ASP 开发人员会疯狂地使用 ASP 脚本。我会听到这样的话，“既然我可以用 VBScript 直接编写 COM 对象，为什么还要等 COM 开发人员来创建它呢？”通过使用标记库，Struts 有助于限制 JSP 文件中所需的 Java 代码的数量。Logic Tag 就是这样的一种库，它对有条件地生成输出进行管理，但这并不能阻止 UI 开发人员对 Java 代码的狂热。无论您决定使用哪种类型的框架，您都应该了解您要在其中部署和维护该框架的环境。当然，这项任务真是说起来容易做起来难。 • 有限的适用范围 Struts 是一种基于 Web 的 MVC 解决方案，所以必须用 HTML、JSP 文件和 servlet 来实现它。 • J2EE 应用程序支持 Struts 需要支持 JSP 1.1 和 Servlet 2.2 规范的 servlet 容器。仅凭这一点远不能解决您的全部安装问题，除非使用 Tomcat 3.2。我用 Netscape iPlanet 6.0 安装这个库时遇到一大堆问题，按理说它是第一种符合 J2EE 的应用程序服务器。我建议您在遇到问题时访问 Struts 用户邮件列表的归档资料。 • 复杂性在将问题分为几个部分的同时也引入了复杂性。毫无疑问，要理解 Struts 必须接受一定的培训。随着变化的不断加入，这有时会令人很沮丧。欢迎访问本网站。 Struts 的前景在这个软件开发的新时代，一切都变得很快。在不到 5 年的时间内，我已经目睹了从 cgi/perl 到 ISAPI/NSAPI、再到使用 VB 的 ASP、一直到现在的 Java 和 J2EE 的变迁。Sun 正在尽力将新的变化反映到 JSP/servlet 体系结构中，正如他们对 Java 语言和 API 所作的更改一样。您可以从 Sun 的网站获得新的 JSP 1.2 和 Servlet 2.3 规范的草案。此外，一个标准 JSP 标记库即将出现。 3：外文出处 [1]Malcolm Davis. Struts——an open-source MVC implementation [2]IBM System Journal,2006

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