如何巧妙处理enq: TX - index contention问题？

导读：数据库表空间扩容是我们在运维过程中经常需要做的事情，常用的方法有增加表空间数据文件或resize数据文件等，本文分享一起使用resize datafile扩容表空间时偶遇enq: TX - index contention引起系统异常的特殊案例，供大家参考。

问题描述

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某客户生产系统核心库在2019-08-21 23:50:00左右出现了业务告警，应用无法连接的情况。

查看故障期间数据库的告警日志，发现在23:49:56，数据库进行了数据库文件扩容操作。

Wed Aug 21 23:49:56 2019
ALTER DATABASE DATAFILE xxxxxxx RESIZE 100G
Wed Aug 21 23:51:38 2019
Completed: ALTER DATABASE DATAFILE xxxxxxx RESIZE 100G
Wed Aug 21 23:52:31 2019
ALTER DATABASE DATAFILE xxxxxxx RESIZE 950G
Thu Aug 22 00:05:23 2019
Completed: ALTER DATABASE DATAFILE xxxxxxx RESIZE 950G
Thu Aug 22 00:15:18 2019

查看故障期间数据库的监听日志，发现从23:58:44到00:05:23这段时间内，数据库没有新的JDBC连接进来。

专家解答

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查看故障期间的ash信息，发现在应用异常的时间段内，SQL_ID为g64z3fw1nffvj的insert操作产生了大量的enq: TX - index contention等待，并且造成这个等待事件的原因就是alter database操作和它本身的insert操作，在resize的执行过程中enq: TX - index contention等待事件一直升高，resize操作成功后（即2019-08-22 00:05:00左右）等待事件恢复正常。

查看相关的trace文件信息：

*** 2019-08-21 23:57:14.907
===============================================================================
HANG ANALYSIS:
  instances (db_name.oracle_sid): xxxxx
  
===============================================================================
 
Chains most likely to have caused the hang<<<<<<<<<<<<<<<<<<<<<<查看HANG住三个可能因素
 [a] Chain 1 Signature: <not in a wait><='buffer busy waits'<='enq: TX - index contention'
     Chain 1 Signature Hash: 0xbeca5ef7
 [b] Chain 2 Signature: <not in a wait><='buffer busy waits'<='enq: TX - index contention'
     Chain 2 Signature Hash: 0xbeca5ef7
 [c] Chain 3 Signature: <not in a wait><='row cache lock'
     Chain 3 Signature Hash: 0xccefbfc0
 
===============================================================================
Non-intersecting chains:
 
-------------------------------------------------------------------------------
Chain 1:
-------------------------------------------------------------------------------
    Oracle session identified by:
    {
                instance: 2 (xxxxx)
                   os id: 15343
              process id: 67
              session id: 2882
        session serial #: 39285
    }
    is waiting for 'enq: TX - index contention' with wait info:
    {
                      p1: 'name|mode'=0x54580004
                      p2: 'usn<<16 | slot'=0x470000
                      p3: 'sequence'=0xa32a2d
  ……
    and is blocked by
 => Oracle session identified by:
    {
                instance: 2 (xxxxxxx)
                   os id: 105251
              process id: 79
              session id: 3400       <<<<<<<<<<<<<<<<<<<<<<chain 1被session_id=3400会话阻塞了
        session serial #: 22853
    }
    which is not in a wait:
    {
               last wait: 36.074155 sec ago
                blocking: 4 sessions
            wait history:
              1.       event: 'ASM file metadata operation'
                 time waited: 0.000018 sec (last interval)
                 time waited: 0.001953 sec (total)
                     wait id: 94              p1: 'msgop'=0x21
                                              p2: 'locn'=0x0
              * time between wait #1 and #2: 0.000000 sec
              2.       event: 'KSV master wait'
                 time waited: 0.001856 sec
                     wait id: 96              
              * time between wait #2 and #3: 0.000000 sec
              3.       event: 'ASM file metadata operation'
                 time waited: 0.000003 sec (last interval)
                 time waited: 0.000079 sec (total)
                     wait id: 94              p1: 'msgop'=0x21
                                              p2: 'locn'=0x0
    }
Chain 1 Signature: <not in a wait><='buffer busy waits'<='enq: TX - index contention'
Chain 1 Signature Hash: 0xbeca5ef7
-------------------------------------------------------------------------------
 
===============================================================================
Intersecting chains:
 
-------------------------------------------------------------------------------
Chain 2:
-------------------------------------------------------------------------------
    Oracle session identified by:
    {
                instance: 2 (xxxxxxx)
                   os id: 70061
              process id: 69
              session id: 2969
        session serial #: 46127
    }
    …….
    and is blocked by 'instance: 2, os id: 83344, session id: 2840',
    which is a member of 'Chain 1'. <<<<<<<<<<<<<<<<<<<<<<被chain1阻塞了 
 
Chain 2 Signature: <not in a wait><='buffer busy waits'<='enq: TX - index contention'
Chain 2 Signature Hash: 0xbeca5ef7
-------------------------------------------------------------------------------
 
-------------------------------------------------------------------------------
Chain 3:
-------------------------------------------------------------------------------
    Oracle session identified by:
    {
                instance: 2 (xxxxxx)
                   os id: 102165
              process id: 75
              session id: 3227
        session serial #: 3457
    }
    is waiting for 'row cache lock' with wait info:
    {
                      p1: 'cache id'=0x6
                      p2: 'mode'=0x0
                      p3: 'request'=0x3
            time in wait: 2.020260 sec
      heur. time in wait: 1 min 59 sec
           timeout after: 0.979740 sec
                 wait id: 360
                blocking: 0 sessions
            wait history:
              * time between current wait and wait #1: 0.000015 sec
              1.       event: 'row cache lock'
                 time waited: 3.001099 sec
                     wait id: 359             p1: 'cache id'=0x6
                                              p2: 'mode'=0x0
                                              p3: 'request'=0x3
              * time between wait #1 and #2: 0.000015 sec
              2.       event: 'row cache lock'
                 time waited: 3.000983 sec
                     wait id: 358             p1: 'cache id'=0x6
                                              p2: 'mode'=0x0
                                              p3: 'request'=0x3
              * time between wait #2 and #3: 0.000013 sec
              3.       event: 'row cache lock'
                 time waited: 3.000978 sec
                     wait id: 357             p1: 'cache id'=0x6
                                              p2: 'mode'=0x0
                                              p3: 'request'=0x3
    }
    and is blocked by 'instance: 2, os id: 105251, session id: 3400'。
    which is a member of 'Chain 1'. <<<<<<<<<<<<<<<<<<<<<<被session_id 3400阻塞了
 
Chain 3 Signature: <not in a wait><='row cache lock'
Chain 3 Signature Hash: 0xccefbfc0
-------------------------------------------------------------------------------
 
===============================================================================
Extra information that will be dumped at higher levels:
[level  4] :   1 node dumps -- [LEAF] [LEAF_NW] 
[level  5] :   4 node dumps -- [NO_WAIT] [INVOL_WT] [SINGLE_NODE] [NLEAF] [SINGLE_NODE_NW] 
State of ALL nodes
 [2839]/2/2840/17657/0x13d1a33000/83344/NLEAF/[3399]
[2881]/2/2882/39285/0x13c1a48b38/15343/NLEAF/[2839]
[2968]/2/2969/46127/0x13b1a69c08/70061/NLEAF/[2839]
[3226]/2/3227/3457/0x13c1ade618/102165/NLEAF/[3399]
[3399]/2/3400/22853/0x1391b4cad8/105251/LEAF_NW/
*** 2019-08-21 23:57:14.908
===============================================================================
END OF HANG ANALYSIS
===============================================================================
*** 2019-08-21 23:58:53.765
Suspected Hangs in the System
                     Root       Chain Total               Hang               
  Hang Hang          Inst Root  #hung #hung  Hang   Hang  Resolution         
    ID Type Status   Num  Sess   Sess  Sess  Conf   Span  Action             
 ----- ---- -------- ---- ----- ----- ----- ------ ------ -------------------
      1 HANG    VALID    2  3400     3   286   HIGH  LOCAL Terminate Process 
<<<<<<<<<<<<<<<<<<< 系统阻塞的可能原因是session id为3400的本地进程引起的
  inst# SessId  Ser#     OSPID Event
  ----- ------ ----- --------- -----
      2      2 19927    111623 enq: TX - index contention
      2   2840 17657     83344 buffer busy waits
      2   3400 22853    105251 not in wait
 
*** 2019-08-21 23:58:53.766
HM: Short Stack of immediate waiter session ID 2840, OSPID 83344 of hang ID 1
Short stack dump:
ksedsts()+465<-ksdxfstk()+32<-ksdxcb()+1927<-sspuser()+112<-__sighandler()<-semtimedop()+10<-skgpwwait()+178<-ksliwat()+2022<-kslwaitctx()+163<-kcbzwb()+1548<-kcbgcur()+8885<-ktfbhget()+254<-ktfbfsearch()+300<-ktfbtgex()+1240<-ktsxs_add()+2094<-ktspnr_next()+1115<-ktrsexec()+529<-ktspbmphwm()+1236<-ktspmvhwm()+53<-ktsp_bump_hwm()+212<-ktspgsp_main()+1941<-kdisnew()+279<-kdisnewle()+115<-kdisle()+4332<-kdiins0()+34743<-kdiinsp()+91<-kauxsin()+1784<-qesltcLoadIndexList()+922<-qesltcLoadIndexes()+55<-qerltcNoKdtBufferedInsRowCBK()+374<-qerltcSingleRowLoad()+279<-qerltcFetch()+379<-insexe()+691<-opiexe()+5632<-kpoal8()+2380<-opiodr()+917<-ttcpip()+2183<-opitsk()+1710<-opiino()+969<-opiodr()+917<-opidrv()+570<-sou2o()+103<-opimai_real()+133<-ssthrdmain()+265<-main()+201<-__libc_start_main()+253

HM: Short Stack of root session ID 3400, OSPID 105251 of hang ID 1
Short stack dump:
ksedsts()+465<-ksdxfstk()+32<-ksdxcb()+1927<-sspuser()+112<-__sighandler()<-pwrite(

从上述trace文件可以看出系统HANG住的可能原因是session_id为 3400的会话引起的。根据查看dba_hist_active_sess_history视图可以看出session_id为 3400的会话就是alter database datafile resize的操作。

根据该故障现象，查询mos发现：Alter Tablespace Resize on Bigfile Tablespace Causes Sessions to Hang with ‘Enq: TX - contention’ and ‘Buffer busy waits’ (Doc ID 2089689.1) ，说明ORACLE 11.2.0.4及后续版本中存在该BUG，调整表空间大小时将阻塞表空间中的其他DDL操作。

问题解决

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• 建议在数据库负载较低的时候进行数据文件扩容

• 建议每次表空间扩容的大小不要过大

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