分类目录归档：Oracle性能优化

library cache pin说明
library cache pin 事件是用来管理library cache的并发访问的, pin一个object会引起相应的heap被载入内存中,如果客户端需要修改或检测这个object它就必须在锁住后取得一个pin.library cache pin的等待时间为3秒钟,其中有1秒钟用于PMON后台进程,即在取得pin之前最多等待3秒钟,否则就超时.library cache pin通常是发生在编译或重新编译PL/SQL,VIEW,TYPES等object时.编译通常都是显性的,如安装应用程序,升级,安装补丁程序等,但object的重新编译也可能发生在object变得无效时.library cache pin的参数如下,有用的主要是P1和P2:
P1 – KGL Handle address.
P2 – Pin address
P3 – 10*Mode + Namespace
其中,P1,P2可与x$kglpn和x$kglob表相关.x$kglpn和x$kglob是ORACLE数据库的内部数据字典.
x$kglpn library cache pin信息
x$kglob library cache object信息

查询方法一

--通过查询V$SESSION_WAIT找出正在等待”library cache pin”的session
SELECT sid,
       SUBSTR (event, 1, 30),
       TO_CHAR(p1, 'xxxxxxxx') p1_16,
       --P1RAW P1_16,
       p2,
       p3
  FROM v$session_wait
 WHERE wait_time = 0 AND event LIKE 'library cache pin%';
--P1 列是Library Cache Handle Address
--P2 列是Library Cache Pin Address. 

--找到相关session pin状态
SELECT ADDR,
       INDX,
       KGLPNADR,-- Library Cache Pin Address
       KGLPNUSE,
       KGLPNSES,--识别锁住此pin 的session
       KGLPNHDL,--Library Cache Handle Address
       kGLPNLCK,
       KGLPNMOD,-- Pin 锁 
       KGLPNREQ-- Pin 请求
  FROM x$kglpn
 WHERE KGLPNHDL LIKE '%EB3EB8%';--p1_16
 
 --询X$KGLOB (Library Cache Object),可找到相关的object
SELECT KGLNAOBJ-- 相关object的名字(取前面80个字符)
  FROM X$KGLOB
 WHERE KGLHDADR LIKE '%EB3EB8%';--p1_16
 
 --查出占着pin锁的session目前正在做什么
SELECT a.sid, a.username, a.program
  FROM v$session a, x$kglpn b
 WHERE a.saddr = b.kglpnuse AND b.kglpnhdl LIKE '%EB3EB8%'--p1_16
  AND b.kgnmod <> 0;
  
   --查出阻塞者正执行的SQL语句
 SELECT sid, sql_text
  FROM v$session, v$sqlarea
 WHERE v$session.sql_address = v$sqlarea.address AND sid =&sid;

查询方法二

--通过查询DBA_LOCK_INTERNAL和V$SESSION_WAIT,可得到与”library cache pin” 等待相关的object的名字
SELECT TO_CHAR (SESSION_ID, '999') sid,
       SUBSTR (LOCK_TYPE, 1, 30) TYPE,
       SUBSTR (lock_id1, 1, 23) Object_Name,
       SUBSTR (mode_held, 1, 4) HELD,
       SUBSTR (mode_requested, 1, 4) REQ,
       lock_id2 Lock_addr
  FROM dba_lock_internal
 WHERE mode_requested <> 'None' AND mode_requested <> mode_held
       AND session_id IN
              (SELECT sid
                 FROM v$session_wait
                WHERE wait_time = 0 AND event LIKE 'library cache pin%');
                
 --查出”library cache pin”占有者(即阻塞者)的session id
 SELECT sid Holder,
       KGLPNUSE Sesion,
       KGLPNMOD Held,
       KGLPNREQ Req
  FROM sys.x$kglpn, v$session
 WHERE KGLPNHDL IN (SELECT p1raw
                      FROM v$session_wait
                     WHERE wait_time = 0 AND event LIKE 'library cache pin%')
       AND KGLPNMOD <> 0
       AND v$session.saddr = x$kglpn.kglpnuse;
       
 --查出”library cache pin”占有者(阻塞者)正在等什么
 SELECT sid, SUBSTR (event, 1, 30), wait_time
  FROM v$session_wait
 WHERE sid IN
          (SELECT sid
             FROM x$kglpn, v$session
            WHERE KGLPNHDL IN
                     (SELECT p1raw
                        FROM v$session_wait
                       WHERE wait_time = 0
                             AND event LIKE 'library cache pin%')
                  AND KGLPNMOD <> 0
                  AND v$session.saddr = x$kglpn.kglpnuse);
                  
 --查出阻塞者正执行的SQL语句
 SELECT sid, sql_text
  FROM v$session, v$sqlarea
 WHERE v$session.sql_address = v$sqlarea.address AND sid =&sid;