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CURSOR_SPACE_FOR_TIME 参数废弃

根据Oracle Metalink文档 Note：565424.1，CURSOR_SPACE_FOR_TIME 参数已经被Oracle放弃。

最先放弃的版本是：10.2.0.5 and 11.1.0.7
在早期的版本中，用户可以通过设置这个参数为True，使得Oracle使用更多的Shared SQL Area去保存SQL，从而提高反复执行SQL解析的速度。
然而随着Oracle Mutexes Pin机制的引入，用户已经几乎不再会从这个参数中受益，加上在某些特定的环境下，这个参数可能会导致严重Bug，随意最终，这个参数被废弃。

在文档中，这个参数的说明大致如下：

CURSOR_SPACE_FOR_TIME lets you use more space for cursors in order to save time. It affects both the shared SQL area and the client's private SQL area.

Values True means take the benifits of this parameter,With True setting Shared SQL areas are kept pinned in the shared pool. As a result, shared SQL areas are not aged out of the pool as long as an open cursor references them. Because each active cursor's SQL area is present in memory, execution is faster. However, the shared SQL areas never leave memory while they are in use. Therefore, you should set this parameter to TRUE only when the shared pool is large enough to hold all open cursors simultaneously.

In addition, a setting of TRUE retains the private SQL area allocated for each cursor between executions instead of discarding it after cursor execution, saving cursor allocation and initialization time

所有使用了这个参数的数据库应当注意。

而且作为一个法则，我应当提醒的是：除非具有了深入的了解与认识，否则不要设置一些不常见、你不了解的参数。

By eygle on 2008-10-11 08:38 | Comments (1) | Beginner | OraNews | 2054 |

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