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Re: pg 9.1 brings host machine down

From: Konstantin Mikhailov <ekimka(at)gmail(dot)com>
To: Patric Bechtel <patric(dot)bechtel(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: pg 9.1 brings host machine down
Date: 2012-06-08 17:52:58
Message-ID: CABDd6w_c9=-KyOCpxD3nsyigzeKBbpP4KzEgK4H9UcZwmyGS4w@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
Thanks alot. I've tried to play with work_mem and after few days
of the production testing pg behaves much better. See no more
files in the pgsql_tmp folder. pg processes consumes reasonable
memory, no swap operation any more. I've studied official pg
docs about work_mem an still have no idea which optimal value
work_mem should have. 1MB is obviously too small. I've increased
up to 32m. due to a lot of the sorts and hash joins in the queries.


On Wed, Jun 6, 2012 at 6:40 PM, Patric Bechtel <patric(dot)bechtel(at)gmail(dot)com>wrote:

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> Hi,
>
> which fs with which settings are you using? What's the work_mem settings?
> Which size do the files
> have?
>
> Depending on the answer of above questions I would suggest:
> - - RAM disk, SSD or separate disk for pgsql_tmp
> - - using xfs with
> noatime,nodiratime,delaylog,logbufs=8,logbsize=256k,nobarrier for the tmp
> area
> - - separating pg_xlog on yet another disk (xfs, too, but with barrier)
> - - using deadline scheduler for all database disks
> - - increasing work_mem to at least the "common" file size +50%
>
> there's more if I'd know more about the setup.
>
> hth,
>
> Patric
>
> Vitalii Tymchyshyn schrieb am 06.06.2012 14:25:
> > Hello.
> >
> > Seen this already. It looks like cross join + sort. Badly configured ORM
> tools like Hibernate
> > with multiple one-to-many relationships fetched with 'join' strategy may
> produce such result.
> > Unfortunately I don't know if it's possible to protect from such a case
> at server side.
> >
> > Best regards, Vitalii Tymchyshyn
> >
> > 06.06.12 15:05, Konstantin Mikhailov написав(ла):
> >> I'm faced with a problem running postgres 9.1.3 which seems to nobody
> else see before. Tried
> >> to search and only one relevant post fond (about millions of files in
> pgsql_tmp).
> >>
> >> Sympthoms:
> >>
> >> Some postgres process size is getting abnormally big compared to other
> postgres processes.
> >> Top shows the 'normal' pg processed is about VIRT 120m, RES ~30m and
> SHR ~30m. That one is
> >> about 6500m, 3.4g, 30m corresp. Total RAM avail - 8g. When one more
> such a process appears
> >> the host going into deep swap and pg restart can help only (actually
> the stop won't even stop
> >> such a process - after shutdown it still alive and can be only killed).
> >>
> >> base/pgsql_tmp contains millions of files. In this situation stop and
> dirty restart is
> >> possible - the normal startup is impossible either. Read somewhere that
> it tries to delete (a
> >> millions files) from that directory. I can't even imagine when it
> finish the deletion so i'm
> >> simple move that folder outside the base - then start can succeed.
> >>
> >> on ubuntu 11.10,12.04 x64. cpu intel core Q9650 3GHz. 8G RAM.
> >>
> >> Does anybody see that behaviour or maybe have some glue how to handle
> it.
> >>
> >> PS: the my preliminary conclusion: some sql is produces a lot of files
> in the temporary table
> >> spaces - very quickly. When sql is finished postgres tries to cleanup
> the folder reading all
> >> contents of the folder and removing the files one by one. It does the
> removal slow (watched
> >> the folder by `find pgsql_tmp | wc -l') but process still consumes the
> RAM. Next such sql
> >> will be a killer :(
> >>
> >>
> >
> >
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