Re: asynch descriptor resize wait event
- From: "April Sims" <sims@xxxxxxx>
- To: "Yong Huang" <yong321@xxxxxxxxx>
- Date: Tue, 01 Jun 2010 08:41:24 -0600
Yong,
It turns out this was not the issue...severe performance degradation
due to optimizer_index_cost_adj and optimizer_index_caching were not set
to default.
Once that was fixed the waits disappeared. The incorrect settings were
due to recommendations by a third party vendor.
Thanks
April Sims
SELECT IOUG Contributing Editor
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sims@xxxxxxx
940-484-4276
>>> Yong Huang <yong321@xxxxxxxxx> 5/21/2010 9:22 AM >>>
April,
If you decide to open an SR, please remember to post what the analyst
says to the list, or at least email me. I'm curious. Thank you.
Yong Huang
--- On Thu, 5/20/10, April Sims <sims@xxxxxxx> wrote:
From: April Sims <sims@xxxxxxx>
Subject: Re: asynch descriptor resize wait event
To: yong321@xxxxxxxxx
Date: Thursday, May 20, 2010, 3:05 PM
Yong,
Thanks
April
>>> Yong Huang <yong321@xxxxxxxxx> 5/20/2010 2:42 PM >>>
The only meaningful note on MOS I can find is 1081977.1. "This event is
set when the number of asynch descriptor reserved inside the OS kernel
has to be readjusted." On Linux, the number of system-wide AIO's is
capped by /proc/sys/fs/aio-max-nr and its current value is aio-nr. I'm
guessing after the said event occurs, /proc/sys/fs/aio-max-nr is raised.
If so, and if the event happens often, it may be a good idea to manually
raise aio-max-nr (echo some_large_number > /proc/sys/fs/aio-max-nr).
Yong Huang
-----Original message-----
This undocumented wait event is recorded when there is an underlying
IO descriptors (kiocb in linux?) needs to be adjusted. During the
time all the pending IOs are suspended momentarily and resumed after
the structure is expanded. I am not sure why this happens in an
otherwise idle database. Perhaps a bug?
On Wed, May 19, 2010 at 3:48 PM, April Sims <sims@xxxxxxx> wrote:
> Anyone know what is causing "asynch descriptor resize" wait events
on
> 11gR2.(11.2.0.1)..on a test database which is mostly idle?
> Linux RH 4 - 64bit
>
> I can only find a limited amount of information on MOS and hardly
anything
> in the Internet.
>
> Hanging in SQLPLUS when querying dba_autotask_client which led me to
search
> for wait events.
>
> thanks
>
> April Sims
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