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latch: In memory undo latch

2010816POMS数据库服务器出现资源耗尽,现象为CPU耗尽,而虚拟内存和I/O均很小,所以判断ORACLE DB出现了CPU密集行等待事件,

查看v$session_wait查看等待事件。

SQL> select sid,EVENT from v$session_wait where WAIT_CLASS<>‘Idle’;

 

       SID EVENT

———- —————————————————————-

       990 latch: In memory undo latch

      1013 latch: In memory undo latch

      1019 latch: In memory undo latch

      1025 latch: In memory undo latch

      1026 latch: In memory undo latch

      1034 SQL*Net message to client

      1035 latch: undo global data

      1062 latch: In memory undo latch

      1068 latch: shared pool

      1084 latch: In memory undo latch

     

  同时ORACLE监控工具得出的结果为:

Top 5 Timed Events

Event

Waits

Time(s)

Avg Wait(ms)

% Total Call Time

Wait Class

CPU time

 

9,929

 

35.7

 

latch: In memory undo latch

40,875

4,305

105

15.5

Concurrency

log file sync

57,607

1,442

25

5.2

Commit

latch: cache buffers chains

9,847

921

94

3.3

Concurrency

log file parallel write

111,766

724

6

2.6

System I/O

latch: In memory undo latch占于一个高位

以前并没有遇到过这个等待事件,所以查看METALINK得出如下结果:

 

Bug 5751672 – “In memory undo latch” contention from kturimugur [ID 5751672.8]  

 

——————————————————————————–

 

  修改时间 12-DEC-2008     类型 PATCH     状态 PUBLISHED  

 

Bug 5751672  “In memory undo latch” contention from kturimugur

 This note gives a brief overview of bug 5751672.

 The content was last updated on: 12-DEC-2008

 Click here for details of each of the sections below.

 

Affects:

Product (Component) Oracle Server (Rdbms)

Range of versions believed to be affected Versions < 11 

Versions confirmed as being affected 10.1.0.5

10.2.0.3

 

Platforms affected Generic (all / most platforms affected)

 

Fixed:

This issue is fixed in 10.2.0.4 (Server Patch Set)

11.1.0.6 (Base Release)

 

 

Symptoms: Related To:

Performance Affected (General)

Waits for “latch free”

 (None Specified)

_IN_MEMORY_UNDO

 

 

Description

“In memory undo latch” contention from kturimugur.

 

Workaround:

  Disable in memory undo (_in_memory_undo=false)

Please note: The above is a summary description only. Actual symptoms can vary. Matching to any symptoms here does not confirm that you are encountering this problem. Always consult with Oracle Support for advice.

 

根据METALINK说明这是一个BUG。需要修改隐含参数进行修复。

 

 

 

 

 

 

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