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Shared SQL Areas (88)

原创 数据库开发技术 作者:tsinglee 时间:2007-10-24 11:12:15 0 删除 编辑

A shared SQL area contains the parse tree and execution plan for a
given SQL statement. Oracle saves memory by using one shared SQL area for SQL
statements run multiple times, which often happens when many users run the same
Oracle allocates memory from the shared pool when a new SQL statement is parsed, to
store in the shared SQL area. The size of this memory depends on the complexity of
the statement. If the entire shared pool has already been allocated, Oracle can
deallocate items from the pool using a modified LRU (least recently used) algorithm
until there is enough free space for the new statement’s shared SQL area. If Oracle
deallocates a shared SQL area, the associated SQL statement must be reparsed and
reassigned to another shared SQL area at its next execution.

1. 包括一个SQL语句的解析树, 执行计划.
2. Oracle为共享内存区域分配内存是在一个新的SQL语句被解析时并被保存在该区域时.分配的内存大小视SQL语
3. 如果该区域全被分配, Oracle使用LRU算法来回收各条款直到有足够的空闲空间for新的SQL.
4. 如果回收了一个共享内存区域, 则相应的SQL在下次执行时会诶重新解析并被指定到另一块共享SQL区域


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