You're welcome.
It might not be absolutely necessary to kill all the processes, just the mutex
holder. There might be a single process spinning on CPU and blocking others.
You can select program,event2 (not program2) with Tanel Poder's ashtop script
to verify it. When killing processes, be aware that pmon (I think) will crash
the database when a critical process is gone. You need to know the critical
ones when you engage in this.
With regard to stack analysis, it's mostly about searching MOS with the
functions from the stack. It's important to explicitly include "Bugs", as
that's not the default, and the bug notes contain the most useful information.
I also lookup the function annotations in Frits Hoogland's http://orafun.info/ ;.
It's critical to identify the stacks where the process spends most time. With
oradebug short_stack you rely on luck that captured stacks are representative.
A more accurate approach would include high frequency sampling on the OS level
and a profiler.
The ultimate game with understanding Oracle C functions would be reverse
engineering with disassembler and decompiler, but that's forbidden by the
license agreement.
Best regards,
Nenad
From: Hameed, Amir <amir.hameed@xxxxxxxxxxxxxxx>
Sent: Mittwoch, 14. Juli 2021 18:46
To: Noveljic Nenad <nenad.noveljic@xxxxxxxxxxxx>; oracle-l@xxxxxxxxxxxxx
Subject: RE: [EXTERNAL] RE: AQ process waiting on "library cache: mutex X"
Thank you for taking the time and looking into this issue.
The only change made to this database was that the STREAMS_POOL_SIZE parameter
was dynamically set a few days ago to address this issue. However, even after
setting the pool, the behavior did not change and we kept seeing Qnn waiting on
the library cache mutex X wait. I even tried killing Qnn processes one at a
time but that didn't help. After your last response, what I did was to kill all
Qnn processes along with the QMNC process (this is a QA env). Once they were
all killed and respawned, the issue seems to have gone away.
Is there a MOS note that contains information on interpreting the call stack?
Thanks,
Amir
[Noveljic Nenad]
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