Oracle9i中的一个特殊等待事件


很多人也许并不清楚,null event其实不是空事件,因为不是没有等待事件,而是Oracle忘记了刚才等待的事件的名字具体是什么了,但却保留了该事件的真实情况。Oracle的开发人员直到9.2.0.3才更新了这些事件的名称。

  那是不是我们每当遇到性能问题的时候都要patch到9.2.0.3呢?

  我们已经知道他的真实情况依然在v$session_wait的p1、p2、p3参数里体现,所以,我们可以根据这些参数,找出这个null event究竟是什么等待事件。

  相关信息:

  1. lck processes to pick up extra or missed 'posts' (messages)。

  in all cases that can be identified the wait time is zero,

  although on most ports this is changed to 1/100th second in

  order to force the process to be rescheduled.

  2. multiple db writers.

  two cases:

  - when the master has sent i/o requests to the slaves, it

  waits on this event for up to 6 seconds until the slaves

  signal that the i/o is complete.

  - the slaves wait on this event for up to 3 seconds whilst

  waiting for requests from the master db writer.

  目前已经被证实的会涉及到null event

  的等待事件还有有sql.net message to client、

  db file scattered (or sequential) read

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