今天在 ORACLE ALLSTAR群里讨论了一个关于队列锁死锁检测的问题，原帖子在这里。 有同学指出对于enqueue lock的死锁检测应当是每3 秒钟检测一次，这样说的依据是通过一个简单可重复的实验可以证明在实际出现ora-00060 dead lock错前process等待了3s:

SQL> select * from v$version;BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bi
PL/SQL Release 10.2.0.5.0 - Production
CORE    10.2.0.5.0      Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - ProductionSQL> select * from global_name;GLOBAL_NAME
--------------------------------------------------------------------------------
www.oracledatabase12g.comPROCESS A:set timing on;
update maclean1 set t1=t1+1;PROCESS B:update maclean2 set t1=t1+1;PROCESS A:
update maclean2 set t1=t1+1;PROCESS B:update maclean1 set t1=t1+1;等待3s后 PROCESS A 会报ERROR at line 1:
ORA-00060: deadlock detected while waiting for resourceElapsed: 00:00:03.02

可以看到Process A在检测到死锁之前确实等待了 3s，而且这是一个可以重复的实验，很具有说服力。 事实真的是这样的吗？   来看下面的演示：

SQL> col name for a30
SQL> col value for a5
SQL> col DESCRIB for a50
SQL> set linesize 140 pagesize 1400
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.ksppdesc describ2   FROM SYS.x$ksppi x, SYS.x$ksppcv y3   WHERE x.inst_id = USERENV ('Instance')4   AND y.inst_id = USERENV ('Instance')5   AND x.indx = y.indx6  AND x.ksppinm='_enqueue_deadlock_scan_secs';NAME                           VALUE DESCRIB
------------------------------ ----- --------------------------------------------------
_enqueue_deadlock_scan_secs    0    deadlock scan intervalSQL> alter system set "_enqueue_deadlock_scan_secs"=18 scope=spfile;System altered.Elapsed: 00:00:00.01SQL> startup force;
ORACLE instance started.Total System Global Area  851443712 bytes
Fixed Size                  2100040 bytes
Variable Size             738198712 bytes
Database Buffers          104857600 bytes
Redo Buffers                6287360 bytes
Database mounted.
Database opened.PROCESS A:SQL> set timing on;
SQL> update maclean1 set t1=t1+1;1 row updated.Elapsed: 00:00:00.06Process BSQL> update maclean2 set t1=t1+1;1 row updated.SQL>  update maclean1 set t1=t1+1;Process A:
SQL>
SQL> alter session set events '10704 trace name context forever,level 10:10046 trace name context forever,level 8';Session altered.SQL> update maclean2 set t1=t1+1;
update maclean2 set t1=t1+1*
ERROR at line 1:ORA-00060: deadlock detected while waiting for resource

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本文转自maclean_007 51CTO博客，原文链接:http://blog.51cto.com/maclean/1278333