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深入理解shared pool共享池之library cache的library cache lock系列四

背景

  本文了解下等待事件library cache lock,进一步理解library cache,之前的文章请见:
  深入理解shared pool共享池之library cache的library cache pin系列三 
 http://blog.itpub.net/9240380/viewspace-1845911/

相关图例

  为了真观理解library cache pin及library cache lock的联系,有个图:
深入理解shared pool共享池之library cache的library cache lock系列四
 

结论

1,道理同library cache pin一样,诊断library cache lock也要使用v$session及dba_kgllock
2, library cache lock是由于library cache pin所引发的,即后者是原因
    因为如果会话想修改或查看对象,必须对对象持锁后获取一个PIN,即先要获取library cache pin,然后才是library cache lock
3, 从DUMP LIBRARY CACHE的结构来看,
可见基于前文:多了lock waiters结构,从LIBRARY CACHE LOCK的含义可见,必须先要获取LIBRARY CACHE PIN,方可获取到LIBRARY CACHE LOCK,现在明显LIBRARY CACHE PIN被其它会话占用,所以获取不到,
只有等待,这样就产生了LIBRARY CACHE LOCK,也就是说只要产生LIBRARY CACHE LOCK,必然存在LIBRARY CACHE PIN,而如果出现LIBRARY CACHE PIN,不一定会出现LIBRARY CACHE LOCK  


4,所以在产生LIBRARY CACHE PIN要马上处理,以防在业务高期连锁出现library cache lock,最终把业务拖死
5,当然上述我们只是从原理来分析下library cache pin及library cache lock,可以直接采用如下脚本,直接找到原因(不过你明白了LIBRARY CACHE的原因,会更有助于解决与此相关的故障)
当然你直接通过blocking_session也可以更为真观直接找到引发library cache lock的元凶,直观原因是library cache pin,最后原因是执行存储过程
也可以说明library cache lock不是latch,而是锁lock
SQL> select sid,serial#,saddr,event,blocking_session from v$session where sid in (111,116,121);


       SID    SERIAL# SADDR            EVENT                          BLOCKING_SESSION
---------- ---------- ---------------- ------------------------------ ----------------
       111        101 00000000A4720168 library cache lock                          121
       116        153 00000000A4726CC0 SQL*Net message from client
       121        215 00000000A472D818 library cache pin                           116
6,library cache lock和library cache pin一样,不是LATCH,它是LOCK锁




测试



library cache lock的含义:
1,用于管理并发访问library cache
2,pinning一个对象,即会把HEAP加载到内存中,也就是说获取到PIN后,方可把HEAP加载到内存中
3,如果会话想修改或查看对象,必须对对象持锁后获取一个PIN,即先要获取library cache pin,然后才是library cache lock




在上述前文的继续,如果新开一个会话编译存储过程,则会产生library cache lock


SQL> select sid from v$mystat where rownum=1;


       SID
----------
       111


SQL> alter procedure proc_hard_parse compile;


SQL> select sid,event,p1,p2,p3 from v$session_wait where sid in (116,121,111);


       SID EVENT                                                                    P1         P2         P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       111 library cache lock                                               2739958280 2664431712        301
       116 SQL*Net message from client                                      1650815232          1          0
       121 library cache pin                                                2739958280 2663017352        301


--查询与library cache lock相关的LATCH
SQL> select latch#,name from v$latch where lower(name) like '%library cache lock%';


    LATCH# NAME
---------- --------------------------------------------------
       218 library cache lock
       221 library cache lock allocation       


--library cache lock LATCH的信息
SQL> select latch#,name from v$latch_children where lower(name) like '%library cache lock%';


    LATCH# NAME
---------- ------------------------------
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock
       218 library cache lock




SQL> select name,parameter1,parameter2,parameter3,wait_class from v$event_name where lower(name) like '%library cache lock%';


NAME                           PARAMETER1                     PARAMETER2                     PARAMETER3                     WAIT_CLASS
------------------------------ ------------------------------ ------------------------------ ------------------------------ --------------------
library cache lock             handle address                 lock address                   100*mode+namespace             Concurrency




---解决LIBRARY CACHE LOCK的脚本


---第1步
可见LIBRARY CACHE LOCK及LIBRARY CACHE PIN皆是基于LIBRARY CACHE HANDLE
SQL> select sid,event,p1,p2,p3 from v$session_wait where sid in (116,121,111);


       SID EVENT                                                                    P1         P2         P3
---------- ---------------------------------------------------------------- ---------- ---------- ----------
       111 library cache lock                                               2739958280 2664431712        301    ---library cache lock
       116 SQL*Net message from client                                      1650815232          1          0
       121 library cache pin                                                2739958280 2663017080        301


---第2步,转换上述的P1为16进制
SQL> select to_char('2739958280','xxxxxxxx') from dual;


TO_CHAR('
---------
 a3507208


--第3步,传入上述的P1到如下字典,找到等待及持有LIBRARY CACHE LOCK的信息(请注意列:KGLLKMOD及KGLKREQ的2个列,道理同于V$LOCK的REQUEST及LMODE)


SQL> select kgllkuse,kgllkhdl,kgllkmod,kgllkreq,kgllktype from dba_kgllock where kgllkhdl='00000000A3507208' and kgllktype='Lock';


KGLLKUSE         KGLLKHDL           KGLLKMOD   KGLLKREQ KGLL
---------------- ---------------- ---------- ---------- ----
00000000A4720168 00000000A3507208          0          3 Lock  --等待library cache lock者
00000000A4726CC0 00000000A3507208          1          0 Lock  
00000000A472D818 00000000A3507208          3          0 Lock  ---持有library cache lock者




--第4步找到library cache lock的引发者,即library cache pin(关于library cache pin,请见我本文开始的之前的前文) 
SQL> select sid,serial#,event from v$session where saddr='00000000A472D818';


       SID    SERIAL# EVENT
---------- ---------- ------------------------------
       121        215 library cache pin


再整合下上述的SQL脚本






当然你直接通过blocking_session也可以更为真观直接找到引发library cache lock的元凶,直观原因是library cache pin,最后原因是执行存储过程
也可以说明library cache lock不是latch,而是锁lock
SQL> select sid,serial#,saddr,event,blocking_session from v$session where sid in (111,116,121);


       SID    SERIAL# SADDR            EVENT                          BLOCKING_SESSION
---------- ---------- ---------------- ------------------------------ ----------------
       111        101 00000000A4720168 library cache lock                          121
       116        153 00000000A4726CC0 SQL*Net message from client
       121        215 00000000A472D818 library cache pin                           116




再从library cache bucket这个维度分析下,可见基于前文:多了lock waiters结构,从LIBRARY CACHE LOCK的含义可见,必须先要获取LIBRARY CACHE PIN,方可获取到LIBRARY CACHE LOCK,现在明显LIBRARY CACHE PIN被其它会话占用,所以获取不到,
只有等待,这样就生了LIBRARY CACHE LOCK,也就是说只要产生LIBRARY CACHE LOCK,必然存在LIBRARY CACHE PIN,而如果出现LIBRARY CACHE PIN,不一定会出现LIBRARY CACHE LOCK
BUCKET 59215:
  LIBRARY OBJECT HANDLE: handle=a3507208 mtx=0xa3507338(0) lct=33 pct=32 cdp=0
  name=SCOTT.PROC_HARD_PARSE 
  hash=84bc90d61f9452e79e7fe2d54c82e74f timestamp=11-24-2015 02:02:36
  namespace=TABL flags=KGHP/TIM/SML/[02000000]
  kkkk-dddd-llll=0000-001d-20bf lock=X pin=S latch#=9 hpc=000c hlc=000c
  lwt=0xa35072b0[0x9ed00090,0x9ed00090] ltm=0xa35072c0[0xa35072c0,0xa35072c0]
  pwt=0xa3507278[0x9eba6d50,0x9eba6d50] ptm=0xa3507288[0xa3507288,0xa3507288]
  ref=0xa35072e0[0xa35072e0,0xa35072e0] lnd=0xa35072f8[0xa34de600,0xa34fed28]
    DEPENDENCY REFERENCES:
    reference latch flags
    --------- ----- -------------------
     98cf88c8     2 DEP[01] whr=0 timestamp=11-24-2015 02:02:36
    LOCK OWNERS:
        lock     user  session count mode flags
    -------- -------- -------- ----- ---- ------------------------
    9ebc9b28 a472d818 a472d818     1 X    [00]  --可以关联DBA_KGLLOCK及V$SESSION找到引发LIBRARY CACHE LOCK的直接原凶,即上述的121会话,可见持有排它锁
    9eb3d748 a4726cc0 a4726cc0     1 N    PNC/[400]  --这是个是最终的原凶,因为最初这个会话是持有NULL模式的LOCK锁,即上述的116会话,可见持有NULL锁
    9eb3d3b0 a4726cc0 a4726cc0     0 N    [4044]   
    LOCK WAITERS:
        lock     user  session count mode
    -------- -------- -------- ----- ----
    9ed00060 a4720168 a4720168     0 X       
    PIN OWNERS:
         pin     user  session     lock count mode mask
    -------- -------- -------- -------- ----- ---- ----
    9eae0b98 a4726cc0 a4726cc0 9eb3d748     3 S    0011
    PIN WAITERS:
         pin     user  session     lock count mode mask
    -------- -------- -------- -------- ----- ---- ----
    9eba6d20 a472d818 a472d818        0     0 X    0000
    LIBRARY OBJECT: object=9d949488
    type=PRCD flags=EXS/LOC[0005] pflags=NST[0001] status=VALD load=0
    DEPENDENCIES: count=3 size=16
    dependency#    table reference   handle position flags
    ----------- -------- --------- -------- -------- -------------------
              0 9d94b210  9d94af50 a3a1b6f0        0 DEP[01]
              1 9d94b210  9d94afa8 a351ce38       33 DEP[01]
              2 9d94b210  9d94b000 a3929db0        0 DEP[01]
    READ ONLY DEPENDENCIES: count=1 size=16
    dependency#    table reference   handle flags
    ----------- -------- --------- -------- -------------------
              0 9d9288d0  9d9285e8 a34fa2c8 /ROD[20]
    ACCESSES: count=1 size=16
    dependency# types
    ----------- -----
              1 0009
    TRANSLATIONS: count=1 size=16
    original    final
    -------- --------
    a351ce38 a351ce38
    DATA BLOCKS:
    data#     heap  pointer    status pins change whr alloc(K)  size(K)
    ----- -------- -------- --------- ---- ------ --- -------- --------
        0 a3507148 9d9495a0 I/P/A/-/-    0 NONE   00      0.37     1.09
        2 9d9497a0 977456b0 I/-/A/-/-    0 NONE   00     13.27    16.00
        4 9d928540 97b67850 I/P/A/-/-    1 NONE   00      2.26     4.00
  BUCKET 59215 total object count=1

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