排查等待latch event
select t2.event,
round(100 * t2.time_waited / (t1.w1 + t3.cpu), 2) event_wait_percent
from (SELECT SUM(time_waited) w1
FROM v$system_event
WHERE event NOT IN
('smon timer',
'pmon timer',
'rdbms ipc message',
'Null event',
'parallel query dequeue',
'pipe get',
'client message',
'SQL*Net message to client',
'SQL*Net message from client',
'SQL*Net more data from client',
'dispatcher timer',
'virtual circuit status',
'lock manager wait for remote message',
'PX Idle Wait',
'PX Deq: Execution Msg',
'PX Deq: Table Q Normal',
'wakeup time manager',
'slave wait',
'i/o slave wait',
'jobq slave wait',
'null event',
'gcs remote message',
'gcs for action',
'ges remote message',
'queue messages',
'wait for unread message on broadcast channel',
'PX Deq Credit: send blkd',
'PX Deq: Execute Reply',
'PX Deq: Signal ACK',
'PX Deque wait',
'PX Deq Credit: need buffer',
'STREAMS apply coord waiting for slave message',
'STREAMS apply slave waiting for coord message',
'Queue Monitor Wait',
'Queue Monitor Slave Wait',
'wakeup event for builder',
'wakeup event for preparer',
'wakeup event for reader',
'wait for activate message',
'PX Deq: Par Recov Execute',
'PX Deq: Table Q Sample',
'STREAMS apply slave idle wait',
'STREAcapture process filter callback wait for ruleset',
'STREAMS fetch slave waiting for txns',
'STREAMS waiting for subscribers to catch up',
'Queue Monitor Shutdown Wait',
'AQ Proxy Cleanup Wait',
'knlqdeq',
'class slave wait',
'master wait',
'DIAG idle wait',
'ASM background timer',
'KSV master wait',
'EMON idle wait',
'Streams AQ:RACqmn coordinator idle wait',
'Streams AQ: qmn coordinator idle wait',
'Streams AQ: qmn slave idle wait',
'Streams AQ: waiting for time management or cleanup tasks',
'Streams AQ: waiting for messages in the queue',
'Streams fetch slave: waiting for txns',
'Streams AQ:deallocate messages from Streams Pool',
'Streams AQ: delete acknowledged messages',
'LNS ASYNC archive log',
'LNS ASYNC dest activation',
'LNS ASYNC end of log',
'LogMiner: client waiting for transaction',
'LogMiner: slave waiting for activate message',
'LogMiner: wakeup event for builder',
'LogMiner: wakeup event for preparer',
'LogMiner: wakeup event for reader')) t1,
(select *
from (select t.event,
t.total_waits,
t.total_timeouts,
t.time_waited,
t.average_wait,
rownum num
from (select event,
total_waits,
total_timeouts,
time_waited,
average_wait
from v$system_event
where event not in
('smon timer',
'pmon timer',
'rdbms ipc message',
'Null event',
'parallel query dequeue',
'pipe get',
'client message',
'SQL*Net message to client',
'SQL*Net message from client',
'SQL*Net more data from client',
'dispatcher timer',
'virtual circuit status',
'lock manager wait for remote message',
'PX Idle Wait',
'PX Deq: Execution Msg',
'PX Deq: Table Q Normal',
'wakeup time manager',
'slave wait',
'i/o slave wait',
'jobq slave wait',
'null event',
'gcs remote message',
'gcs for action',
'ges remote message',
'queue messages',
'wait for unread message on broadcast channel',
'PX Deq Credit: send blkd',
'PX Deq: Execute Reply',
'PX Deq: Signal ACK',
'PX Deque wait',
'PX Deq Credit: need buffer',
'STREAMS apply coord waiting for slave message',
'STREAMS apply slave waiting for coord message',
'Queue Monitor Wait',
'Queue Monitor Slave Wait',
'wakeup event for builder',
'wakeup event for preparer',
'wakeup event for reader',
'wait for activate message',
'PX Deq: Par Recov Execute',
'PX Deq: Table Q Sample',
'STREAMS apply slave idle wait',
'STREAcapture process filter callback wait for ruleset',
'STREAMS fetch slave waiting for txns',
'STREAMS waiting for subscribers to catch up',
'Queue Monitor Shutdown Wait',
'AQ Proxy Cleanup Wait',
'knlqdeq',
'class slave wait',
'master wait',
'DIAG idle wait',
'ASM background timer',
'KSV master wait',
'EMON idle wait',
'Streams AQ: RAC qmn coordinator idle wait',
'Streams AQ: qmn coordinator idle wait',
'Streams AQ: qmn slave idle wait',
'Streams AQ: waiting for time management or cleanup tasks',
'Streams AQ: waiting for messages in the queue',
'Streams fetch slave: waiting for txns',
'Streams AQ:deallocate messages from Streams Pool',
'Streams AQ: delete acknowledged messages',
'LNS ASYNC archive log',
'LNS ASYNC dest activation',
'LNS ASYNC end of log',
'LogMiner: client waiting for transaction',
'LogMiner: slave waiting for activate message',
'LogMiner: wakeup event for builder',
'LogMiner: wakeup event for preparer',
'LogMiner: wakeup event for reader')
order by time_waited desc) t)
where num < 11) t2,
(SELECT VALUE CPU
FROM v$sysstat
WHERE NAME LIKE 'CPU used by this session') t3;
当存在latch event的时候，很容易的通过v$session_wait视图查到是哪些会话产生的：
select sid,seq#,event from v$session_wait
如果需要具体确定热点对象，可以通过v$latch_children中查询具体的子latch信息
SELECT * FROM (SELECT addr, child#, gets, misses, sleeps, immediate_gets igets, immediate_misses imiss, spin_gets sgets FROM v$latch_children WHERE NAME = 'cache buffers chains' ORDER BY sleeps DESC) WHERE ROWNUM < 11;
亦可以通过以下语句获取最热数据库的latch和buffer信息
SELECT b.addr, a.ts#, a.dbarfil, a.dbablk, a.tch, b.gets, b.misses, b.sleeps FROM (SELECT * FROM (SELECT addr, ts#, file#, dbarfil, dbablk, tch, hladdr FROM x$bh ORDER BY tch DESC) WHERE ROWNUM < 11) a, (SELECT addr, gets, misses, sleeps FROM v$latch_children WHERE NAME = 'cache buffers chains') b WHERE a.hladdr = b.addr
可以找到这些热点buffer的对象信息：
SELECT distinct e.owner, e.segment_name, e.segment_type FROM dba_extents e, (SELECT * FROM (SELECT addr, ts#, file#, dbarfil, dbablk, tch FROM x$bh ORDER BY tch DESC) WHERE ROWNUM < 11) b WHERE e.relative_fno = b.dbarfil AND e.block_id <= b.dbablk AND e.block_id + e.blocks > b.dbablk;
结合v$sqltext或v$sqlarea可以找到对象的相关SQL：
break on hash_value skip 1 SELECT /*+ rule */ hash_value, sql_text FROM v$sqltext WHERE (hash_value, address) IN (SELECT a.hash_value, a.address FROM v$sqltext a, (SELECT DISTINCT a.owner, a.segment_name, a.segment_type FROM dba_extents a, (SELECT dbarfil, dbablk FROM (SELECT dbarfil, dbablk FROM x$bh ORDER BY tch DESC) WHERE ROWNUM < 11) b WHERE a.relative_fno = b.dbarfil AND a.block_id <= b.dbablk AND a.block_id + a.blocks > b.dbablk) b WHERE a.sql_text LIKE '%' || b.segment_name || '%' AND b.segment_type = 'TABLE') ORDER BY hash_value, address, piece