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分类: Oracle
2013-01-06 15:36:09
The first of these is often the default, and in Oracle 7.1 is the only option available.via the buffer cache (and then DBWR) Using sort direct writes
In Oracle 7.2 the parameter SORT_DIRECT_WRITES can be set to cause processes to write sort blocks direct to disk avoiding the buffer cache. It is generally desirable to set SORT_DIRECT_WRITES to TRUE to ensure sort blocks do not impact the buffer cache.
Note 1: Setting SORT_DIRECT_WRITES=TRUE causes additional memory to be allocated for the session.
Note 2: In a lightly loaded environment SORT_DIRECT_WRITES may cause an individual job to take slightly longer ! Consider that when blocks are placed in the buffer cache it is acting almost like a memory extension to that process as "GETs" of sort blocks may be satisfied from the cache rather than from disk.
Since Oracle 8.1 the parameter SORT_DIRECT_WRITES became obsolete and direct writes are always used for sort operations that do not fit into the sort area size.