Re: Fun with WAIT Event "library cache: mutex X"
- From: Gaja Krishna Vaidyanatha <gajav@xxxxxxxxx>
- To: "ChrisDavid.Taylor@xxxxxxxxxxxxxxx" <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>, "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 8 Dec 2011 10:24:37 -0800 (PST)
Hi Chris,
Just curious - are you using automatic SGA memory management?
In my humble experience, I have seen the mutex waits that you refer to when
resize operations happen at bad times (basically stealing away from the shared
pool to give to the database buffer cache more memory because of a spurt of
high I/O requests). In those cases, I have actually turned off automatic SGA
memory management in exchange of stability and consistency. Not to mention the
problem just goes away. I am big believer in automating the appropriate
components in my database (thank you Oracle for automating among other
components - UNDO :) ).
But, I am still old school when it comes to buffer cache sizing, shared pool &
other pools sizing. I believe it should be part of a DBA's job and should be
automated ONLY in applications/databases that demonstrate consistent,
predictable and static behavior in workloads. For more dynamic and inconsistent
workloads, I personally would go with manual memory settings. It is worthwhile
incurring the additional cost of allocating more memory for the required
structures and gain stability and consistency in return. Plus, the CPU overhead
of MMAN (if and where relevant) can be avoided.
Cheers,
Gaja
Gaja Krishna Vaidyanatha,
CEO & Founder, DBPerfMan LLC
http://www.dbperfman.com
http://www.dbcloudman.com
Phone - +1-650-743-6060
http://www.linkedin.com/in/gajakrishnavaidyanathaCo-author:Oracle
Insights:Tales of the Oak Table
- http://www.apress.com/book/bookDisplay.html?bID14
Co-author:Oracle Performance Tuning 101
- http://www.amazon.com/gp/reader/0072131454/ref=sib_dp_pt/102-6130796-4625766
________________________________
From: "Taylor, Chris David" <ChrisDavid.Taylor@xxxxxxxxxxxxxxx>
To: "'oracle-l@xxxxxxxxxxxxx'" <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, December 8, 2011 8:45 AM
Subject: Fun with WAIT Event "library cache: mutex X"
I'm running 11.2.0.2 Patch 10 on Windows x64 and I have a pl/sql procedure that
is rather simple, but kept erroring out after some time with an out memory
condition.
So, I decided to look and see what it is doing and it is encountering the
"library cache: mutex X" event.
Browing Oracle Support, I found the note about it and it says:
* "P3 = "where" = location in code (internal identifier) where mutex is being
waited for
@The meaning of the code for "where" can be found by looking in kgl0.h for
entries with the prefix ""kglml_XXX". For example, if P3=2, then it
corresponds to "kglml_kglget2". You can then search source code for this
symbol to see where the mutex is acquired.
Well, that's not very helpful to me since I don't have access to the source
code :) I understand that the engineers can use it.
Long story short, I decided to download the 11.2.0.3 patchset.
It is only *4 GIGABYTES*. I'm getting about 170k download speed on my work
network so......
Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
"Quality is never an accident; it is always the result of intelligent effort."
-- John Ruskin (English Writer 1819-1900)
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