记一则update 发生enq: TX - row lock contention 的处理方法
根据事后在虚拟机中复现客户现场发生的情况，做一次记录（简化部分过程，原理不变）
客户端1执行update语句
SQL> select * from test; ID NAME ---------- -------------------------------- 2 b 10 c 1 b SQL> update test set id = 3 where name = 'c'; 1 row updated.
客户端2执行另外一条update语句
SQL> update test set id = 4 where name = 'c';
这个时候第二条update卡住了，证明发生了hanganalyze，查询当前的等待事件
SQL> select vw.sid,v.serial#, vw.event, vw.p1raw, vw.p2, v.username, sql_id from v$session_wait vw, v$session v where vw.sid = v.sid and vw.event not like '%message%' order by 3 desc; SID SERIAL# EVENT P1RAW P2 USERNAME SQL_ID ---------- ---------- -------------------------------------------------- ---------------- ---------- --------------- ------------- 13 1 smon timer 000000000000012C 0 2 1 pmon timer 000000000000012C 0 40 7 i/o slave wait 0000000091605340 0 42 23 i/o slave wait 0000000091605340 0 36 23 enq: TX - row lock contention 0000000054580006 196608 ELAN 53msja8m8hbcw 4 1 VKTM Logical Idle Wait 00 0 31 3 Streams AQ: waiting for time management or cleanup 00 0 tasks 18 15 Streams AQ: qmn slave idle wait 0000000000000001 0 25 9 Streams AQ: qmn coordinator idle wait 00 0 33 43 Space Manager: slave idle wait 00 0 8 1 DIAG idle wait 0000000000000005 1 6 1 DIAG idle wait 0000000000000005 1 12 rows selected.
可以看到等待事件中有tx锁
进而查找彼此发生的依赖关系，是谁堵塞了谁
SELECT DECODE(request,0,'Holder: ','Waiter: ')||sid sess, id1, id2, lmode, request, type FROM V$LOCK WHERE (id1, id2, type) IN(SELECT id1, id2, type FROM V$LOCK WHERE request>0) ORDER BY id1, request; SESS ID1 ID2 LMODE REQUEST TY ------------------------------------------------ ---------- ---------- ---------- ---------- -- Holder: 46 196608 786 6 0 TX Waiter: 36 196608 786 0 6 TX
发现，持有者是46号sid，等待着是36号sid，并且lmode模式是6
在oracle官方的支持文档中可以看到对于该模式的描述 exclusive 独占(X)：独立访问使用，exclusive，通常发生在Alter table, Drop table, Drop Index, Truncate table, Lock Exclusive
进而可以根据sid查找是那条语句发生了阻塞
SELECT /*+ ORDERED */ a.SQL_TEXT FROM v$sqltext a WHERE (a.hash_value, a.address) IN ( SELECT DECODE (sql_hash_value, 0, prev_hash_value, sql_hash_value ), DECODE (sql_hash_value, 0, prev_sql_addr, sql_address) FROM v$session b where b.SID = 46) order by a.PIECE SQL_TEXT ---------------------------------------------------------------- update test set id = 3 where name = 'c'
进而可以根据sid和serial反查是那个机器发出了这条指令
select sid,serial#,machine,CLIENT_INFO from v$session where sid = 2 '46'; SID SERIAL# MACHINE CLIENT_INFO ---------- ---------- ---------------------------------------------------------------- ---------------------------------------------------------------- 46 67 elan
基本就能够排查所出现情况，进而进行沟通解决，是不是语句未提交导致，或者是其他原因
等待持有锁的会话commit或者rollback。 通常为会话1在某行上执行 update/delete 未提交，会话2对同一行数据进行 update/delete，或其它原因（例如SQL性能差）造成的锁释放速度缓慢或网络问题，都会造成后续的会话进入队列等待
不着急查杀，这个还是要等待确认后，在进行下一步操作
接下里我们使用hanganalyze来分析上述问题
执行hanganalyze
SQL> ORADEBUG setmypid Statement processed. SQL> oradebug unlimit; Statement processed. SQL> oradebug hanganalyze 3 Hang Analysis in /u01/app/oracle/diag/rdbms/elan/elan/trace/elan_ora_6322.trc SQL>
HANG ANALYSIS基本信息，摘录部分信息如下
------------------------------------------------------------------------------- Chain 1: ------------------------------------------------------------------------------- Oracle session identified by: --阻塞会话信息 { instance: 1 (elan.elan) os id: 6337 process id: 27, oracle@elan (TNS V1-V3) session id: 36 session serial #: 23 } is waiting for 'enq: TX - row lock contention' with wait info: { p1: 'name|mode'=0x54580006 p2: 'usn<<16 | slot'=0x30000 p3: 'sequence'=0x312 time in wait: 19 min 57 sec timeout after: never wait id: 24 blocking: 0 sessions --此处显示当前会话没有阻塞的session，说明是被阻塞会话 current sql: update test set id = 4 where name = 'c' wait history: * time between current wait and wait #1: 0.000966 sec 1. event: 'db file sequential read' time waited: 0.000178 sec wait id: 23 p1: 'file#'=0x5 p2: 'block#'=0x8a time waited: 0.000040 sec wait id: 22 p1: 'FileOperation'=0x2 p2: 'fileno'=0x5 p3: 'filetype'=0x2 * time between wait #2 and #3: 0.001004 sec 3. event: 'SQL*Net message from client' time waited: 17.589536 sec wait id: 21 p1: 'driver id'=0x62657100 p2: '#bytes'=0x1 } and is blocked by => Oracle session identified by: { instance: 1 (elan.elan) os id: 6336 process id: 25, oracle@elan (TNS V1-V3) session id: 46 --会话session session serial #: 67 } which is waiting for 'SQL*Net message from client' with wait info: { p1: 'driver id'=0x62657100 p2: '#bytes'=0x1 time in wait: 20 min 21 sec timeout after: never wait id: 25 blocking: 1 session --此处显示被阻塞的会话数是1，也证明是锁会话持有者 current sql: <none> short stack: ksedsts()+465<-ksdxfstk()+32<-ksdxcb()+1927<-sspuser()+112<-__sighandler()<-read()+14<-ntpfprd()+117<-nsbasic_brc()+376<-nsbrecv()+69<-nioqrc()+495<-opikndf2()+978<-opitsk()+831<-opiino()+969<-opiodr()+917<-opidrv()+570<-sou2o()+103<-opimai_real()+133<-ssthrdmain()+265<-main()+201<-__libc_start_main()+253 wait history: * time between current wait and wait #1: 0.000003 sec 1. event: 'SQL*Net message to client' time waited: 0.000001 sec wait id: 24 p1: 'driver id'=0x62657100 p2: '#bytes'=0x1 * time between wait #1 and #2: 0.000069 sec 2. event: 'Disk file operations I/O' time waited: 0.000040 sec wait id: 23 p1: 'FileOperation'=0x2 p2: 'fileno'=0x3 p3: 'filetype'=0x2 * time between wait #2 and #3: 0.000287 sec
通过上述分析:大概可以得出sid=36因为请求enq: TX - row lock contention(TX mode=6)被sid=46阻塞
分析过程基本如上
