快速了解Oracle 9i中的一个特殊等待事件
2007-09-20 12:40:06 来源:WEB开发网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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