2010年8月16日POMS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
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。
