一、概述：
阻塞是DBA经常碰到的情形，尤其是不良的应用程序设计所造成的阻塞将导致数据库性能的严重下降，直至数据库崩溃。对DBA而言，有必要知道如何定位到当前系统有哪些阻塞，到底谁是阻塞者，谁是被阻塞者。本文对此给出了描述并做了相关演示。

二、演示阻塞：

--更新表，注，提示符scott@CNMMBO表明用户为scott的session，用户名不同，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) --另起两个session更新同样的行，这两个session都会处于等待，直到第一个session提交或回滚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; --下面在第一个session 查询阻塞情况scott@CNMMBO> @blocker BLOCK_MSG BLOCK-------------------------------------------------- ----------pts/5 ('1073,4642') is blocking 1067,10438 1pts/5 ('1073,4642') is blocking 1065,4464 1--上面的结果表明session 1073,4642 阻塞了后面的2个--即session 1073,4642是阻塞者，后面2个session是被阻塞者 --Author : Leshami--Blog : http://blog.csdn.net/leshami --下面查询正在阻塞的session id，SQL语句以及被阻塞的时间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 --下面的查询阻塞时锁的持有情况 scott@CNMMBO> @request_lock_type USERNAME SID TY LMODE REQUEST ID1 ID2------------------------------ ---------- -- ----------- ----------- ---------- ----------SCOTT 1073 TX Exclusive None 524319 27412LESHAMI 1067 TX None Exclusive 524319 27412GOEX_ADMIN 1065 TX None Exclusive 524319 27412--可以看到LESHAMI，GOEX_ADMIN 2个用户都在请求524319/27412上的Exclusive锁，而此时已经被SCOTT加了Exclusive锁 --查询阻塞时锁的持有详细信息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、文中涉及到的相关SQL脚本完整代码如下：

robin@SZDB:~/dba_scripts/custom/sql> more my_env.sql SELECT spid, s.sid, s.serial#, p.username, p.programFROM v$process p, v$session sWHERE 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$sqlareaSELECT 'sid=' || a.SID || ' Wait Class=' || a.wait_class || ' Time=' || a.seconds_in_wait || CHR (10) || ' Query=' || b.sql_text FROM v$session a, v$sqlarea b WHERE a.blocking_session IS NOT NULL AND a.sql_address = b.addressORDER BY a.blocking_session/robin@SZDB:~/dba_scripts/custom/sql> more request_lock_type.sql--This script generates a report of users waiting for locks.--Access Privileges: SELECT on v$session, v$lockSELECT sn.username, m.sid, m.type, DECODE(m.lmode, 0, 'None', 1, 'Null', 2, 'Row Share', 3, 'Row Excl.', 4, 'Share', 5, 'S/Row Excl.', 6, 'Exclusive', lmode, ltrim(to_char(lmode,'990'))) lmode, DECODE(m.request,0, 'None', 1, 'Null', 2, 'Row Share', 3, 'Row Excl.', 4, 'Share', 5, 'S/Row Excl.', 6, 'Exclusive', request, ltrim(to_char(m.request, '990'))) request, m.id1, m.id2FROM v$session sn, v$lock mWHERE (sn.sid = m.sid AND m.request != 0) OR (sn.sid = m.sid AND m.request = 0 AND lmode != 4 AND (id1, id2) IN (SELECT s.id1, s.id2 FROM v$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.sqlset linesize 190col osuser format a15col username format a20 wrapcol object_name format a20 wrapcol terminal format a25 wrapcol Req_Mode format a20select 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 Cwhere A.OBJECT_ID(+) = B.ID1 and B.SID = C.SID and C.USERNAME is not nullorder by B.SID, B.ID2;