Auto segment management just automates the process by which you used to have to manually
tune using multiple freelists. In the past, you would have had to of determine the
number of concurrent modifiers of data (inserts/updates that happen exactly at about the
same time) and configure multiple freelists in order to satisfy these concurrent requests
in a timely fashion.
With auto management you don't have to do this anymore. It'll not distribute across
multiple blocks any more then multiple freelists would have in the past -- only you need
not waste your time and energy attempting to determine the exact correct number of
freelists to have.
This new feature is more efficient then multiple freelists:
<quote>
Free lists have been the traditional method of managing free space within segments.
Bitmaps, however, provide a simpler and more efficient way of managing segment space.
They provide better space utilization and completely eliminate any need to specify and
tune the PCTUSED, FREELISTS, and FREELISTS GROUPS attributes
for segments created in the tablespace. If such attributes should be specified, they are
ignored.
</quote>
a very informal, quick and dirty test I've done shows that automatic segment space mgmt
gives us almost all of the benfit of finely tuned freelists -- without the pain of finely
tuning freelists (something that is virtually impossible to do in the "real world"
anyway).
Go for it -- on a heavy OLTP type table -- this is very beneficial.
感谢楼上诸位兄弟,小结下,只说性能,管理上优势显而易见:
1. Bigfile在某些可能影响性能的方面做的比Smallfile
Performance of database opens, checkpoints, and DBWR processes should improve if data is stored in bigfile tablespaces instead of traditional tablespaces. However, increasing the datafile size might increase time to restore a corrupted file or create a new datafile.
-- http://download.oracle.com/docs/cd/B19306_01/server.102/b14220/physical.htm#i14068
2. ASM可以改善性能,由上面天黑的回复及
ASM:A vertical integration of both the file system and the volume manager built specifically for Oracle Database files. It extends the concept of stripe and mirror everything to optimize performance, while removing the need for manual I/O tuning.
-- http://download.oracle.com/docs/cd/B28359_01/server.111/b28318/glossary.htm#CNCPT1995
3. 不过上面都是ORACLE自己说的,有时候也当不得真。
4. 所以有没有人明白里面的实现机理或给出测试数据。
5. 此帖200分,哪边给建议都给分,明天结帐,多谢!