enq: TX – row lock/index contention、allocate ITL等待事件enq: TM – contention等待事件Oracle队列锁enq:TS,Temporary Segment (also TableSpace)
tuned undo retention 是自动undo调优特性，见undo自动调优介绍。| UNXPSTEALCNT | NUMBER | Number of attempts to obtain undo space by stealing unexpired extents from other transactions
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| UNXPBLKRELCNT | NUMBER | Number of unexpired blocks removed from certain undo segments so they can be used by other transactions | | UNXPBLKREUCNT | NUMBER | Number of unexpired undo blocks reused by transactions | | EXPSTEALCNT | NUMBER | Number of attempts to steal expired undo blocks from other undo segments | | EXPBLKRELCNT | NUMBER | Number of expired undo blocks stolen from other undo segments | | EXPBLKREUCNT | NUMBER | Number of expired undo blocks reused within the same undo segments | | SSOLDERRCNT | NUMBER | Identifies the number of times the error ORA-01555 occurred. You can use this statistic to decide whether or not the UNDO_RETENTION initialization parameter is set properly given the size of the undo tablespace. Increasing the value of UNDO_RETENTION can reduce the occurrence of this error.
具体见全面解析9i以后Oracle Latch闩锁原理；8i以前的latch算法可以参考：Oracle Latch:一段描绘Latch运作的伪代码
http://www.askmaclean.com/archives/understanding-oracle-mutex.html – – –
Mutex的Get和Sleep
但是请注意在V$MUTEX_SLEEP_*视图上的sleep列意味着等待的次数。相关代码函数在开始进入等待时自加这个sleep字段。
http://www.askmaclean.com/archives/enqueue-tx-row-lock-index-itl-wait-event.html