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Breakable Parse Locks (355)

原创 IT综合 作者:tsinglee 时间:2007-12-12 11:05:58 0 删除 编辑
A SQL statement (or PL/SQL program unit) in the shared pool holds a parse lock for each schema object it references. Parse locks are acquired so that the associated shared SQL area can be invalidated if a referenced object is altered or dropped. A parse lock does not disallow any DDL operation and can be broken to allow conflicting DDL operations, hence the name breakable parse lock. A parse lock is acquired during the parse phase of SQL statement execution and held as long as the shared SQL area for that statement remains in the shared pool. 可解除的解析锁 1. 共享池中的SQL语句获得了引用每个对象的解析锁 2. 当所引用的对象被修改或删除后,此共享 SQL 区被置为无效。解析锁不会禁止任何 DDL 操作 ,当出现与解析锁冲突的 DDL 操作时,解析锁将被解除,因此也称之为可解除的解析锁 3. 解析锁在SQL语句的执行阶段获得 , 在共享SQL被清出共享池前能一直保持[@more@]

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