Re: Oracle 10g hangs intermittently waiting for I/O
- From: Rajeev Prabhakar <rprabha01@xxxxxxxxx>
- To: Paweł Kotlarz <pkotla@xxxxxx>
- Date: Fri, 15 May 2009 18:08:45 -0400
Pawel,
So that I can understand your environment better, could you please answer
these questions :
a) Does the database server's /tmp filesystem have adequate free space ?
b) Is the oracle installation configured with adequate swap space
( I know no sysadmin would like to have additional swap allocated),
however, going with typical oracle specified swap settings have saved me
a lots of headaches (while load/stress testing) (including node freeze/reboots).
c) What is the size of your temp tablespace ? (Allocated and Free space
during typical application usage window) ?
d) Are you (or your application) utilizing GTTs (global temporary tables) ?
e) Are you utilizing huge pages on your database server ?
f) Is this dedicated OR shared server configuration ?
g) Have you looked at the prospect of any soft block corruption for any table ?
I) Any i/o bound concurrent processes (database specific or otherwise) running
during the window when database freeze is being observed ? say - backups
(database OR o.s.)
j) Are there any specific kinds of processes that are first reported
to be getting
hung / experiencing slowness (e.g. reports/html output etc..) ?
-Rajeev
2009/5/15 Paweł Kotlarz <pkotla@xxxxxx>:
> Rajeev,
>
> Oracle shows many sessions waiting for direct path read (temp). Tanel's
> waitprof reports single events taking many seconds though most of
> them are below 15ms.
>
> On the OS level vmstat shows normal reading for some time and then
> sessions in an uninterruptible sleep with no I/O taking place. iostat -x
> and asmiostat (ML 437996.1) show specific volumes. Just after the
> performance returns to normal these volumes show much greater queue
> length (iostat) or much greater average read time (asmiostat).
>
> I ran strace on a process servicing the session on which I used waitprof
> earlier. It stops on a read call.
>
> Currently I only know that the sysadmins found nothing in Linux logs and on
> a 'system management page'. Unfortunately it is difficult to obtain
> more information from them unless I tell what exactly to check...
>
> Thanks,
> Pawel
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