WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK!的分析

今天我的数据库hang住了，查看告警日志提示

WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=31

AIX 5.3 是一个RAC环境，10.2.0.4

由于问题一致，我这边没有把生产环境中日志拿出来，但是我参考一个博文的，具体如下：

1.山西电信告警alert_mega.log

Mon Jun 01 02:50:03 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=31

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_27190.trc

Tue Jun 02 02:50:03 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=32

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_2063.trc

Tue Jun 02 17:53:40 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=37

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_7006.trc

Tue Jun 02 18:00:41 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=38

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_7120.trc

Wed Jun 03 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=39

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_9632.trc

Wed Jun 03 20:54:39 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=41

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_15023.trc

Wed Jun 03 20:55:07 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=42

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_15029.trc

Wed Jun 03 20:55:26 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=43

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_15033.trc

Thu Jun 04 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=44

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_16725.trc

Fri Jun 05 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=45

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_23781.trc

Sat Jun 06 02:50:03 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=46

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_30833.trc

Sat Jun 06 23:50:03 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=47

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_4951.trc

Sun Jun 07 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=48

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_5891.trc

Mon Jun 08 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=49

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_7520.trc

Tue Jun 09 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=50

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_14768.trc

Wed Jun 10 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=51

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_23975.trc

Wed Jun 10 22:24:05 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=52

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_29755.trc

Wed Jun 10 22:25:03 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=53

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_29760.trc

Thu Jun 11 02:50:02 CST 2015

>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=54

System State dumped to trace file /opt/oracle/admin/dba/udump/mega_ora_31040.trc

在TRACE文件中包含一个SYSTEMSTATE DUMP ,首先通过ASS.awk来分析一下systemstate dump:

Resource Holder State

Enqueue PR-00000000-00000000 41: last wait for 'os thread startup'

Latch c0000000c2df3b70 ??? Blocker

Rcache object=c000000f9fdf8160, 61: waiting for 'log file switch (checkpoint incomplete)'

Enqueue US-0000004C-00000000 185: waiting for 'log file switch (checkpoint incomplete)'

Enqueue FB-00000006-0186BDC8 187: waiting for 'log file switch (checkpoint incomplete)'

LOCK: handle=c000000f388db3d0 204: waiting for 'log file switch (checkpoint incomplete)'

Object Names

~~~~~~~~~~~~

Enqueue PR-00000000-00000000

Latch c0000000c2df3b70 holding (efd=5) c0000000c2df3b70 slave cl

Rcache object=c000000f9fdf8160,

Enqueue US-0000004C-00000000

Enqueue FB-00000006-0186BDC8

LOCK: handle=c000000f388db3d0 TABL:REPORT.STATQ_AGENT_SUBS_NEW

看样子ORAPID=41的会话可能是BLOCKER，从ass生成的报告来看，系统中存在大量的log file switch（checkpoint incomplete）等待。我们首先查看一下latch c0000000c2df3b70的持有者：

PROCESS 41:

----------------------------------------

SO: c000000fbe3c1910, type: 2, owner: 0000000000000000, flag: INIT/-/-/0x00

(process) Oracle pid=41, calls cur/top: c000000f9d63cbd0/c000000fa2c63088, flag: (2) SYSTEM

int error: 0, call error: 0, sess error: 0, txn error 0

(post info) last post received: 0 0 33

last post received-location: ksrpublish

last process to post me: c000000fba3f0d80 1 6

last post sent: 0 0 24

last post sent-location: ksasnd

last process posted by me: c000000fb93cbc00 1 6

(latch info) wait_event=0 bits=1

holding (efd=5) c0000000c2df3b70 slave class create level=0

Location from where latch is held: ksvcreate:

Context saved from call: 0

state=busy, wlstate=free

waiters [orapid (seconds since: put on list, posted, alive check)]:

48 (61788, 1251079676, 3)

118 (61728, 1251079676, 0)

waiter count=2

Process Group: DEFAULT, pseudo proc: c000000fbc44e418

O/S info: user: oracle, term: UNKNOWN, ospid: 16929

mmon在等待：

service name: SYS$BACKGROUND

last wait for 'os thread startup' blocking sess=0x0000000000000000 seq=59956 wait_time=1006468 seconds since wait started=62472

=0, =0, =0

Dumping Session Wait History

for 'os thread startup' count=1 wait_time=1006468

for 'os thread startup' count=1 wait_time=958707

for 'os thread startup' count=1 wait_time=1017506

for 'os thread startup' count=1 wait_time=975671

for 'os thread startup' count=1 wait_time=976846

for 'os thread startup' count=1 wait_time=984219

for 'os thread startup' count=1 wait_time=585799

for 'os thread startup' count=1 wait_time=1355858

for 'os thread startup' count=1 wait_time=979583

for 'os thread startup' count=1 wait_time=990744

看样子mmon在启动其他进程的时候在等待启动结束:

SO: c000000f9e6e3a20, type: 16, owner: c000000fbe3c1910, flag: INIT/-/-/0x00

(osp req holder)

CHILD REQUESTS:

(osp req) type=2(BACKGROUND) flags=0x20001(STATIC/-) state=8(DEAD) err=0

pg=129(default) arg1=0 arg2=(null) reply=(null) pname=m000

pid=0 parent=c000000f9e6e3a20 fulfill=0000000000000000

原来mmon在等待m000启动.那么mmon等待m000会导致整个系统HANG住吗？我们需要进一步分析

我们回过头来在来看这个>>> WAITED TOO LONG FOR A ROW CACHE ENQUEUE LOCK! pid=XXX

这个等待从临晨4点多到宕机前一直存在。通过ass的结果，我们可以看到：

254:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

255:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

256:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

257:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

258:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

259:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

260:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

261:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

262:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

263:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

264:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

265:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

266:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

267:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

268:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

269:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

270:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

271:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

272:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

273:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

274:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

275:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

276:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

277:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

278:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

279:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

280:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

281:waiting for 'row cache lock' [Rcache object=c000000f9fdf8160,] wait

检查一下process 254

service name: SYS$USERS

O/S info: user: report, term: , ospid: 17444, machine: qdbb2

waiting for 'row cache lock' blocking sess=0x0000000000000000 seq=1 wait_time=0 seconds since wait started=3425

cache id=7, mode=0, request=3

for 'row cache lock' count=1 wait_time=2615950

for 'row cache lock' count=1 wait_time=2929664

for 'row cache lock' count=1 wait_time=2929674

for 'row cache lock' count=1 wait_time=2929666

SO: c000000f9f9198b8, type: 50, owner: c000000ee30a3060, flag: INIT/-/-/0x00

row cache enqueue: count=1 session=c000000fba59b660 object=c000000f9fdf8160, request=S

savepoint=0x4

row cache parent object: address=c000000f9fdf8160 cid=7(dc_users)

hash=cdb2e447 typ=11 transaction=c000000faae8c710 flags=0000012a

own=c000000f9fdf8230[c000000f9f919a08,c000000f9f919a08] wat=c000000f9fdf8240[c000000f9f9198e8,c000000f9f918b08] mode=X

这是一个dc_users的对象，请求s方式的访问，目前在等待一个mode=x的等待释放，因此我们搜索c000000f9fdf8160, mode=X，找到：

SO: c000000f9f9199d8, type: 50, owner: c000000faae8c710, flag: INIT/-/-/0x00

row cache enqueue: count=1 session=c000000fba5f3b30 object=c000000f9fdf8160, mode=X

savepoint=0x6

row cache parent object: address=c000000f9fdf8160 cid=7(dc_users)

hash=cdb2e447 typ=11 transaction=c000000faae8c710 flags=0000012a

own=c000000f9fdf8230[c000000f9f919a08,c000000f9f919a08] wat=c000000f9fdf8240[c000000f9f9198e8,c000000f9f918b08] mode=X

status=VALID/UPDATE/-/-/IO/-/-/-/-

request=N release=TRUE flags=0

instance lock id=QH b6ae8f92 4cc6da8c

set=0, complete=FALSE

set=1, complete=FALSE

set=2, complete=FALSE

就是这个会话持有了这个dc_users的row cache object，而且持有方式是不兼容的，往前看，发现这个会话是：

PROCESS 61:

SO: c000000fbf3bfe48, type: 2, owner: 0000000000000000, flag: INIT/-/-/0x00

(process) Oracle pid=61, calls cur/top: c000000fa0c0eb30/c000000f8b0fdef8, flag: (0) -

(post info) last post received: 109 0 4

last post received-location: kslpsr

last process to post me: c000000fbc3c2d98 1 6

last process posted by me: c000000fbc3c2d98 1 6

(latch info) wait_event=109 bits=0

O/S info: user: oracle, term: UNKNOWN, ospid: 2006

SO: c000000fba5f3b30, type: 4, owner: c000000fbf3bfe48, flag: INIT/-/-/0x00

(session) sid: 1973 trans: c000000faae8c710, creator: c000000fbf3bfe48, flag: (41) USR/- BSY/-/-/-/-/-

DID: 0001-003D-041A6D36, short-term DID: 0000-0000-00000000

txn branch: 0000000000000000

oct: 0, prv: 0, sql: 0000000000000000, psql: 0000000000000000, user: 0/SYS

O/S info: user: liping, term: L902054, ospid: 163000:163128, machine:

program: plsqldev.exe

application name: plsqldev.exe, hash value=2126984564

waiting for 'log file switch (checkpoint incomplete)' blocking sess=0x0000000000000000 seq=9 wait_time=0 seconds since wait started=2290

for 'log file switch (checkpoint incomplete)' count=1 wait_time=87117

for 'log file switch (checkpoint incomplete)' count=1 wait_time=976593

for 'log file switch (checkpoint incomplete)' count=1 wait_time=979179

for 'log file switch (checkpoint incomplete)' count=1 wait_time=7099

for 'log file switch (checkpoint incomplete)' count=1 wait_time=976471

for 'log file switch (checkpoint incomplete)' count=1 wait_time=976611

for 'log file switch (checkpoint incomplete)' count=1 wait_time=973437

for 'log file switch (checkpoint incomplete)' count=1 wait_time=969860

for 'log file switch (checkpoint incomplete)' count=1 wait_time=976535

for 'log file switch (checkpoint incomplete)' count=1 wait_time=978815

这是一个PL/SQL DEVELOPER的用户，不过从上面的情况看，这个会话是产生了阻塞大量会话的源头，不过这个会话本身也是受害者，在等待log file switch(checkpoint incomplete),为什么会这样呢？

于是我们来看看lgwr的状态：

SO: c000000fba6167c0, type: 4, owner: c000000fbc3c2d98, flag: INIT/-/-/0x00

(session) sid: 2155 trans: 0000000000000000, creator: c000000fbc3c2d98, flag: (51) USR/- BSY/-/-/-/-/-

DID: 0001-0024-00000005, short-term DID: 0000-0000-00000000

waiting for 'rdbms ipc message' blocking sess=0x0000000000000000 seq=13185 wait_time=0 seconds since wait started=0

timeout=d3, =0, =0

for 'control file sequential read' count=1 wait_time=233

file#=0, block#=2e, blocks=1

for 'control file sequential read' count=1 wait_time=210

file#=0, block#=2c, blocks=1

for 'control file sequential read' count=1 wait_time=255

file#=0, block#=29, blocks=1

for 'control file sequential read' count=1 wait_time=213

file#=0, block#=27, blocks=1

for 'control file sequential read' count=1 wait_time=222

file#=2, block#=1, blocks=1

for 'control file sequential read' count=1 wait_time=221

file#=1, block#=1, blocks=1

for 'control file sequential read' count=1 wait_time=282

file#=0, block#=1, blocks=1

for 'rdbms ipc message' count=1 wait_time=4564

timeout=d4, =0, =0

for 'rdbms ipc message' count=1 wait_time=3188

for 'rdbms ipc message' count=1 wait_time=1

LGWR居然在等待ipc message，说明lgwr并没有处于工作状态，或者无事可做，或者等待其他会话处理结束后唤醒它。而目前大家都在等待log file switch，lgwr没有闲着没事做的理由，因此我们有理由相信checkpoint出问题了，lgwr是在等待ckpt完成工作，于是我们继续检查ckpt的状态：

搜索(ckpt)

SO: c000000fbb632130, type: 4, owner: c000000fbb40bc08, flag: INIT/-/-/0x00

(session) sid: 2154 trans: 0000000000000000, creator: c000000fbb40bc08, flag: (51) USR/- BSY/-/-/-/-/-

DID: 0001-0025-00000004, short-term DID: 0001-0025-00000005

waiting for 'enq: PR - contention' blocking sess=0xc000000fbf5e4278 seq=61352 wait_time=0 seconds since wait started=62446

name|mode=50520006, 0=0, 0=0

for 'enq: PR - contention' count=1 wait_time=429069

for 'enq: PR - contention' count=1 wait_time=2929688

for 'enq: PR - contention' count=1 wait_time=2929668

for 'enq: PR - contention' count=1 wait_time=2929682

for 'enq: PR - contention' count=1 wait_time=2929671

for 'enq: PR - contention' count=1 wait_time=2929679

for 'enq: PR - contention' count=1 wait_time=2929666

for 'enq: PR - contention' count=1 wait_time=2929683

for 'enq: PR - contention' count=1 wait_time=2929624

for 'enq: PR - contention' count=1 wait_time=2929676

ckpt一直在等待PR锁，这回我们终于看到了blocking sess=0xc000000fbf5e4278 ，这个会话就是阻塞ckpt的元凶，我们来看看是谁：

SO: c000000fbf5e4278, type: 4, owner: c000000fbe3c1910, flag: INIT/-/-/0x00

(session) sid: 2150 trans: 0000000000000000, creator: c000000fbe3c1910, flag: (100051) USR/- BSY/-/-/-/-/-

DID: 0001-0029-00000002, short-term DID: 0001-0029-00000003

oct: 0, prv: 0, sql: c000000fa3ed29b8, psql: 0000000000000000, user: 0/SYS

我们又找到了mmon，原来mmon才是导致系统HANG住的元凶。

案例总结：

1、到目前为止，我们弄清楚了系统HANG住的主要原因是MMON启动m000的时候，m000没能够正常启动，导致mmon长期持有pr锁，阻塞了ckpt，导致无法正常做日志切换，但是mmon未能正常启动m000的原因还没有找到，这需要更多的资料进行分析，不在本文讨论之内

2、碰到这种问题如何处理？实际上如果我们分析清楚了，只要杀掉mmon进程，或者调整一下一下statistics_level就可能解决问题，而不需要重启实例。但是这个分析需要时间，最起码也需要30-60分钟的分析时间，如果在生产环境下发生，很难给我们这么长的分析时间。但是大家要注意这个问题的出现时在4点多钟，系统HANG住是在10点多钟，中间有很长时间供我们分析。如果我们能及时发现这个异常，是可能在系统HANG住钱解决问题的

本文转自xiaocao1314051CTO博客，原文链接：http://blog.51cto.com/xiaocao13140/1970622 ，如需转载请自行联系原作者

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