背景现象： 应用系统响应速度慢，常因为堵塞锁过多导致系统堵死，应用无法使用。用top命令查看，CPU利用率居高不下
处理过程：
查看oracle的等待事件，select event,count(*) from v$session_wait group by event;发现有21个latch: Cache buffers chains事件，latch是内存的争用导致 确认为latch: cache buffers chains引起的故障后，查看latch的命中率 SQL>SELECT name, gets, misses/gets, sleeps, immediate_gets, immediate_misses FROM v$latch WHERE name = ‘cache buffers chains’;各列名称意义如下
NAME：latch名称 IMMEDIATE_GETS：以Immediate模式latch请求数 GETS：以Willing to wait请求模式latch的请求数 SPIN_GETS：第一次尝试失败，但在以后的轮次中成功 WAIT_TIME：花费在等待latch的时间 这里需要注意MISSES/GETS如果在达10%左右，则说明有比较严重的latch争用
查找问题sql_id
SELECT * FROM (SELECT COUNT(*), SQL_ID, NVL(O.OBJECT_NAME, ASH.CURRENT_OBJ#) OBJN, SUBSTR(O.OBJECT_TYPE, 0, 10) OTYPE, CURRENT_FILE# FN, CURRENT_BLOCK# BLOCKN FROM V$ACTIVE_SESSION_HISTORY ASH, ALL_OBJECTS O WHERE EVENT LIKE 'latch: cache buffers chains' AND O.OBJECT_ID(+) = ASH.CURRENT_OBJ# GROUP BY SQL_ID, CURRENT_OBJ#, CURRENT_FILE#, CURRENT_BLOCK#, O.OBJECT_NAME, O.OBJECT_TYPE ORDER BY COUNT(*) DESC) WHERE ROWNUM <= 10; --sql_id对应sql select sql_fulltext from v$sqlarea where sql_id='&sqlid';找出对应sql语句，分析其执行计划，根据业务进行针对性优化，最终问题解决
