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一、概述：

阻塞是DBA經(jīng)常碰到的情形，尤其是不良的應(yīng)用程序設(shè)計(jì)所造成的阻塞將導(dǎo)致數(shù)據(jù)庫(kù)性能的嚴(yán)重下降，直至數(shù)據(jù)庫(kù)崩潰。對(duì)DBA而言，有必要知道如何定位到當(dāng)前系統(tǒng)有哪些阻塞，到底誰(shuí)是阻塞者，誰(shuí)是被阻塞者。本文對(duì)此給出了描述并做了相關(guān)演示。

二、演示阻塞：

--更新表，注，提示符scott@CNMMBO表明用戶為scott的session，用戶名不同，session不同。

scott@CNMMBO> update emp set sal=sal*1.1 where empno=7788;

1 row updated.

scott@CNMMBO> @my_env

SPID        SID  SERIAL# USERNAME    PROGRAM

------------ ---------- ---------- --------------- ------------------------------------------------

11205       1073    4642 robin      oracle@SZDB (TNS V1-V3)

--另起兩個(gè)session更新同樣的行，這兩個(gè)session都會(huì)處于等待，直到第一個(gè)session提交或回滾

leshami@CNMMBO> update scott.emp set sal=sal+100 where empno=7788;

goex_admin@CNMMBO> update scott.emp set sal=sal-50 where empno=7788;

--下面在第一個(gè)session 查詢阻塞情況

scott@CNMMBO> @blocker

BLOCK_MSG                        BLOCK

-------------------------------------------------- ----------

pts/5 ('1073,4642') is blocking 1067,10438         1

pts/5 ('1073,4642') is blocking 1065,4464          1

--上面的結(jié)果表明session 1073,4642 阻塞了后面的2個(gè)

--即session 1073,4642是阻塞者，后面2個(gè)session是被阻塞者

--Author : Leshami

--Blog  : http://blog.csdn.net/leshami

--下面查詢正在阻塞的session id，SQL語(yǔ)句以及被阻塞的時(shí)間

scott@CNMMBO> @blocking_session_detail.sql

'SID='||A.SID||'WAITCLASS='||A.WAIT_CLASS||'TIME='||A.SECONDS_IN_WAIT||CHR(10)||'QUERY='||B.SQL_TEXT

------------------------------------------------------------------------

sid=1067 Wait Class=Application Time=5995

 Query=update scott.emp set sal=sal+100 where empno=7788

sid=1065 Wait Class=Application Time=225

 Query=update scott.emp set sal=sal-50 where empno=7788

--下面的查詢阻塞時(shí)鎖的持有情況

scott@CNMMBO> @request_lock_type

USERNAME               SID TY LMODE    REQUEST      ID1    ID2

------------------------------ ---------- -- ----------- ----------- ---------- ----------

SCOTT                1073 TX Exclusive  None      524319   27412

LESHAMI               1067 TX None    Exclusive    524319   27412

GOEX_ADMIN              1065 TX None    Exclusive    524319   27412

--可以看到LESHAMI，GOEX_ADMIN 2個(gè)用戶都在請(qǐng)求524319/27412上的Exclusive鎖，而此時(shí)已經(jīng)被SCOTT加了Exclusive鎖

--查詢阻塞時(shí)鎖的持有詳細(xì)信息

scott@CNMMBO> @request_lock_detail

    SID USERNAME       OSUSER     TERMINAL         OBJECT_NAME     TY Lock Mode  Req_Mode

---------- -------------------- --------------- ------------------------- -------------------- -- ----------- --------------------

   1065 GOEX_ADMIN      robin      pts/1           EMP         TM Row Excl

   1065 GOEX_ADMIN      robin      pts/1           Trans-524319     TX --Waiting-- Exclusive

   1067 LESHAMI       robin      pts/0           EMP         TM Row Excl

   1067 LESHAMI       robin      pts/0           Trans-524319     TX --Waiting-- Exclusive

   1073 SCOTT        robin      pts/5           EMP         TM Row Excl

   1073 SCOTT        robin      pts/5           Trans-524319     TX Exclusive

三、文中涉及到的相關(guān)SQL腳本完整代碼如下：

robin@SZDB:~/dba_scripts/custom/sql> more my_env.sql

SELECT spid, s.sid, s.serial#, p.username, p.program

FROM v$process p, v$session s

WHERE p.addr = s.paddr

   AND s.sid = (SELECT sid

          FROM v$mystat

          WHERE rownum = 1);

robin@SZDB:~/dba_scripts/custom/sql> more blocker.sql

col block_msg format a50;

select c.terminal||' ('''||a.sid||','||c.serial#||''') is blocking '||b.sid||','||d.serial# block_msg, a.block

from v$lock a,v$lock b,v$session c,v$session d

 where a.id1=b.id1

 and a.id2=b.id2

 and a.block>0

 and a.sid <>b.sid

 and a.sid=c.sid

 and b.sid=d.SID;

robin@SZDB:~/dba_scripts/custom/sql> more blocking_session_detail.sql

--To find the query for blocking session

--Access Privileges: SELECT on v$session, v$sqlarea

SELECT   'sid='

     || a.SID

     || ' Wait Class='

     || a.wait_class

     || ' Time='

     || a.seconds_in_wait

     || CHR (10)

     || ' Query='

     || b.sql_text

  FROM v$session a, v$sqlarea b

  WHERE a.blocking_session IS NOT NULL AND a.sql_address = b.address

ORDER BY a.blocking_session

/

robin@SZDB:~/dba_scripts/custom/sql> more request_lock_type.sql

--This script generates a report of users waiting for locks.

--Access Privileges: SELECT on v$session, v$lock

SELECT sn.username, m.sid, m.type,

    DECODE(m.lmode, 0, 'None',

            1, 'Null',

            2, 'Row Share',

            3, 'Row Excl.',

            4, 'Share',

            5, 'S/Row Excl.',

            6, 'Exclusive',

        lmode, ltrim(to_char(lmode,'990'))) lmode,

    DECODE(m.request,0, 'None',

             1, 'Null',

             2, 'Row Share',

             3, 'Row Excl.',

             4, 'Share',

             5, 'S/Row Excl.',

             6, 'Exclusive',

             request, ltrim(to_char(m.request,

        '990'))) request, m.id1, m.id2

FROM v$session sn, v$lock m

WHERE (sn.sid = m.sid AND m.request != 0)

    OR (sn.sid = m.sid

        AND m.request = 0 AND lmode != 4

        AND (id1, id2) IN (SELECT s.id1, s.id2

   FROM v$lock s

            WHERE request != 0

       AND s.id1 = m.id1

                AND s.id2 = m.id2)

        )

ORDER BY id1, id2, m.request;

robin@SZDB:~/dba_scripts/custom/sql> more request_lock_detail.sql

set linesize 190

col osuser format a15

col username format a20 wrap

col object_name format a20 wrap

col terminal format a25 wrap

col Req_Mode format a20

select B.SID, C.USERNAME, C.OSUSER, C.TERMINAL,

    DECODE(B.ID2, 0, A.OBJECT_NAME,

      'Trans-'||to_char(B.ID1)) OBJECT_NAME,

   B.TYPE,

    DECODE(B.LMODE,0,'--Waiting--',

           1,'Null',

           2,'Row Share',

           3,'Row Excl',

          4,'Share',

           5,'Sha Row Exc',

      6,'Exclusive',

            'Other') "Lock Mode",

    DECODE(B.REQUEST,0,' ',

           1,'Null',

           2,'Row Share',

           3,'Row Excl',

           4,'Share',

           5,'Sha Row Exc',

           6,'Exclusive',

           'Other') "Req_Mode"

 from DBA_OBJECTS A, V$LOCK B, V$SESSION C

where A.OBJECT_ID(+) = B.ID1

 and B.SID = C.SID

 and C.USERNAME is not null

order by B.SID, B.ID2;

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