library cache lock等待事件

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标题:library cache lock等待事件

作者:惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

Library cache lock介绍
Oracle利用Library cache lock和Library cache pin来实现并发控制,Library cache lock是在handle上获取的,而Library cache pin则是在data heap上获取。访问对象时,首先必须获取handle上的lock,然后将访问的数据pin在内存中。lock的作用是控制进程间的并发访问,而pin的作用是保证数据一致性,防止数据在访问时被交换出去。
lock和pin的实现类似于enqueue,在每个handle上都有lock和pin的holder list和waiter list,用来保存持有该资源和等待该资源的队列。

Library cache lock相关sql语句

--找出library cache lock等待sid,saddr信息
select sid,saddr from v$session where event= 'library cache lock';

SID        SADDR
---------- --------
16         572ed244

--找出blocked信息
select kgllkhdl Handle,kgllkreq Request, kglnaobj Object
from x$kgllk where kgllkses = '572ed244'
and kgllkreq > 0;

HANDLE   REQUEST   OBJECT
-------- ---------- ------------------
62d064dc          2 EMPLOYEES

--找出blocking信息
select kgllkses saddr,kgllkhdl handle,kgllkmod mod,kglnaobj object
from x$kgllk lock_a
where kgllkmod > 0
and exists (select lock_b.kgllkhdl from x$kgllk lock_b
where kgllkses = '572ed244' /* blocked session */
and lock_a.kgllkhdl = lock_b.kgllkhdl
and kgllkreq > 0);

SADDR     HANDLE   MOD         OBJECT
--------  -------- ---------- ------------
572eac94  62d064dc          3  EMPLOYEES

--blocking 会话信息
select sid,username,terminal,program from v$session where saddr = '572eac94'

SID        USERNAME     TERMINAL  PROGRAM
---------- -----------  --------- --------------------------------------------
12          SCOTT        pts/20    sqlplus@goblin.forgotten.realms (TNS V1-V3)

--所有blocked 会话
select sid,username,terminal,program from v$session
where saddr in 
(select kgllkses from x$kgllk lock_a 
 where kgllkreq > 0
 and exists (select lock_b.kgllkhdl from x$kgllk lock_b
             where kgllkses = '572eac94' /* blocking session */
             and lock_a.kgllkhdl = lock_b.kgllkhdl
             and kgllkreq = 0)
);

SID        USERNAME  TERMINAL  PROGRAM
---------- --------- --------- -------------------------------------------
13         SCOTT     pts/22    sqlplus@goblin.forgotten.realms (TNS V1-V3)
16         SCOTT     pts/7     sqlplus@goblin.forgotten.realms (TNS V1-V3)
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library cache lock等待事件》有 1 条评论

  1. 惜分飞 说:

    Systemstate 分析library cache lock持有者和阻塞者

    Systemstate event will create a tracefile containing detailed information on every Oracle process. 
    This information includes all the resources held & requested by a specific process.
    
    While an operation is hanging, open a new session and launch the following statement:
    For Oracle 9.2.0.1 or higher:
    $sqlplus '/ as sysdba'
    oradebug setmypid
    oradebug unlimit
    oradebug dump systemstate 266
    
    For older versions you can use the following syntax that is also possible in higher versions.
    The level 266 is not available before 9.2.0.6
    
    alter session set max_dump_file_size=unlimited;
    alter session set events 'immediate trace name systemstate level 10'
    
     Oracle will create a systemstate tracefile in your USER_DUMP_DEST directory.
    
    Get the PID (ProcessID) of the 'hanging' session:
    
    select pid from v$process where addr=
    (select paddr from v$session where sid= <sid_of_hanging_session> );
    
    The systemstate dump contains a separate section with information for each process. 
    Open the tracefile and do a search for "PROCESS <PID from above>".
    In the process section search for the wait event by doing a search on 'waiting for'.
    
    PROCESS 20: 
    ---------------------------------------- 
    SO: 0x7d2bd820, type: 2, owner: (nil), flag: INIT/-/-/0x00 
    (process) Oracle pid=20, calls cur/top: 0x7d3d62d0/0x7d3d85dc, flag: (0) - 
    int error: 0, call error: 0, sess error: 0, txn error 0 
    (post info) last post received: 109 0 4 
    last post received-location: kslpsr 
    last process to post me: 7d2b8d94 1 6 
    last post sent: 0 0 24 
    last post sent-location: ksasnd 
    last process posted by me: 7d2b8d94 1 6 
    (latch info) wait_event=0 bits=0 
    Process Group: DEFAULT, pseudo proc: 0x7d2ed5dc 
    O/S info: user: oracle, term: pts/7, ospid: 19759 
    OSD pid info: Unix process pid: 19759, image: goblin.forgotten.realms (TNS V1-V3) 
    
    <cut> 
    
    (session) sid: 141 trans: (nil), creator: 0x7d2bd820, flag: (41) USR/- BSY/-/-/-/-/- 
    DID: 0001-0014-00000668, short-term DID: 0000-0000-00000000 
    txn branch: (nil) 
    oct: 6, prv: 0, sql: 0x62d01c34, psql: 0x7c20f24c, user: 542/SCOTT 
    service name: SYS$USERS 
    O/S info: user: oracle, term: pts/7, ospid: 19758, machine: goblin.forgotten.realms 
    program: sqlplus@goblin.forgotten.realms (TNS V1-V3) 
    application name: SQL*Plus, hash value=3669949024 
    waiting for 'library cache lock' blocking sess=0x(nil) seq=36 wait_time=0 seconds since wait started=11 
    handle address=62d064dc, lock address=79f88a68, 100*mode+namespace=c9 
    
    
    •	Use the handle address to find information on the object locked:
    
    SO: 0x79f88a68, type: 53, owner: 0x7d3d62d0, flag: INIT/-/-/0x00
    LIBRARY OBJECT LOCK: lock=79f88a68 handle=62d064dc request=S
    call pin=(nil) session pin=(nil) hpc=0000 hlc=0000
    htl=0x79f88ab4[0x79e71e60,0x79e71e60] htb=0x79e71e60 ssga=0x79e716fc
    user=7d3a13b8 session=7d3a13b8 count=0 flags=[0000] savepoint=0xce
    LIBRARY OBJECT HANDLE: handle=62d064dc mtx=0x62d06590(0) cdp=0
    name=SCOTT.EMPLOYEES 
    
    We see the library object lock is being requested in Shared mode (request=S)
    Name of the the object is SCOTT.EMPLOYEES
    
    
    •	Use the 'handle address' to find the process that is holding the lock on  
    your resource by doing a search on the address within the same tracefile.
    
    PROCESS 18: 
    ---------------------------------------- 
    SO: 0x7d2bcca8, type: 2, owner: (nil), flag: INIT/-/-/0x00 
    (process) Oracle pid=18, calls cur/top: 0x79f3ab84/0x7d3d5fc8, flag: (0) - 
    int error: 0, call error: 0, sess error: 0, txn error 0 
    (post info) last post received: 109 0 4 
    last post received-location: kslpsr 
    last process to post me: 7d2b8d94 1 6 
    last post sent: 0 0 24 
    last post sent-location: ksasnd 
    last process posted by me: 7d2b8d94 1 6 
    
    <cut> 
    
    SO: 0x75fe8f7c, type: 53, owner: 0x7b751914, flag: INIT/-/-/0x00 
    LIBRARY OBJECT LOCK: lock=75fe8f7c handle=62d064dc mode=X 
    call pin=(nil) session pin=(nil) hpc=0000 hlc=0000 
    htl=0x75fe8fc8[0x79f81790,0x79fc3ef8] htb=0x79f81790 ssga=0x79f8102c 
    user=7d3988d0 session=7d3988d0 count=1 flags=[0000] savepoint=0x146e 
    LIBRARY OBJECT HANDLE: handle=62d064dc mtx=0x62d06590(0) cdp=0 
    name=SCOTT.EMPLOYEES
    
    From the output we can see that the Process 18 (pid)  is holding  an exclusive lock (mode=X) 
    on the object we are trying to access. Using V$PROCESS and V$SESSION we can retrieve the sid, 
    user, terminal, program,... for this process.
     
    The actual statement that was launched by this session is also listed in the tracefile
     (statements and other library cache objects are preceded by 'name=').
    

      [引用]  [回复]

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