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Allocation of Temporary Segments for Queries (27)

原创 网络安全 作者:tsinglee 时间:2007-09-13 15:01:20 0 删除 编辑
Oracle allocates temporary segments as
needed during a user session in one of the temporary tablespaces of the user issuing
the statement. Specify these tablespaces with a CREATE USER or an ALTER USER
statement using the TEMPORARY TABLESPACE clause.
If no temporary tablespace is defined for the user, then the default temporary
tablespace is the SYSTEM tablespace. The default storage characteristics of the
containing tablespace determine those of the extents of the temporary segment. Oracle
drops temporary segments when the statement completes.
Because allocation and deallocation of temporary segments occur frequently, create at
least one special tablespace for temporary segments. By doing so, you can distribute
I/O across disk devices, and you can avoid fragmentation of the SYSTEM and other
tablespaces that otherwise hold temporary segments.
Entries for changes to temporary segments used for sort operations are not stored in
the redo log, except for space management operations on the temporary segment.
1. 可通过CREATE USER或者ALTER USER来指定用户的临时表空间
2. 创建一个临时表空间 , 可避免碎片 , 分散I/O
3. 临时段用来排序时 , 不记redo log
4. 在临时段上进行的space management operations记redo log[@more@]

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