null event不是空事件，不是沒有等待事件,而是Oracle忘記了剛才等待的事件的名字是什么了，但保留了該事件的真實情況。Oracle 的開發人員直到9.2.0.3才更新了這些事件名稱。那是不是我們每當碰到性能問題的時候都要patch到9.2.0.3呢？ 我們已經知道他的真實情況依然在v$session_wait的P1、P2、P3參數里體現，所以，我們可以從這些參數順藤摸瓜，找出這個null event;到底是什么等待事件。下面是ITPUB上COPY過來的一些信息：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 inorder to force the process to be rescheduled.2. Multiple DB writers.Two cases:- When the master has sent i/o requests to the slaves, itwaits on this event for up to 6 seconds until the slavessignal that the i/o is complete.- The slaves wait on this event for up to 3 seconds whilstwaiting for requests from the master db writer.目前已經被證實的會涉及到null event 的等待事件還有有SQL*Net message to client、;db file scattered (or sequential) read待續