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Re: [BULK] Problems with vacuum!

From: "Domenico Sgarbossa" <domenico(at)xtecnica(dot)com>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: [BULK] Problems with vacuum!
Date: 2004-06-22 13:33:33
Message-ID: 004d01c4585d$83bc1200$70c8007e@xtecnica.it (view raw or flat)
Thread:
Lists: pgsql-performance
As you suggets I've tried to upgrade to the kernel 2.4.28, but it seems that
nothing change!
I built a new machine with Red Hat 8  (kernel 2.4.28) a 1GB RAM using the
same parameters i've been used before.
After the boot, i've got 800Mb of free memory, if a launch a pg_dump then
the system swap (only 1 or 2 mb.....) and the
free memory become 20mb.
Now, if I tried a vacuumdb the system use partially the cached memory then
begin to swap again.... with 700mb of cached
memory it's very strange that the system swap again....

anyone know why this happend?

Distinti Saluti

Sgarbossa Domenico
X Tecnica S.R.L.
www.xtecnica.com
Tel: 049/9409154 - 049/5970297
Fax: 049/9400288

----- Original Message -----
From: "Scott Marlowe" <smarlowe(at)qwest(dot)net>
To: "Joshua D. Drake" <jd(at)commandprompt(dot)com>
Cc: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>; "Domenico Sgarbossa"
<domenico(at)xtecnica(dot)com>; <pgsql-performance(at)postgresql(dot)org>
Sent: Friday, June 18, 2004 8:58 PM
Subject: Re: [PERFORM] [BULK] Problems with vacuum!


> I believe it was more like the kernel was tuned to make it less common,
> but certain things can still trigger it.  I know the problem was still
> there in the 2.4.24 on the last server I was playing with, but it was a
> lot less of a problem than it had been under 2.4.9 on an earlier machine
> with the same basic amount of memory.
>
> On Fri, 2004-06-18 at 12:47, Joshua D. Drake wrote:
> > Hello,
> >
> > I would have to double check BUT I believe this is fixed in later 2.4.x
> > kernels as well. If you don't want to go through the hassle of 2.6
> > (although it really is a nice kernel) then upgrade to 2.4.26.
> >
> > Sincerely,
> >
> > Joshau D. Drake
> >
> > Scott Marlowe wrote:
> > > On Fri, 2004-06-18 at 09:11, Tom Lane wrote:
> > >
> > >>"Domenico Sgarbossa" <domenico(at)xtecnica(dot)com> writes:
> > >>
> > >>>so when the users go home, i've got something like 15/20000kb free
ram, the
> > >>>rest is cached and 0kb of swap...
> > >>>It seems that when pg_dump starts the cached memory isn't released so
the
> > >>>system begin to swap,
> > >>
> > >>A sane kernel should drop disk buffers rather than swapping.  We heard
> > >>recently about a bug in some versions of the Linux kernel that cause
it
> > >>to prefer swapping to discarding disk cache, though.  It sounds like
> > >>that's what you're hitting.  Look into newer kernels ...
> > >
> > >
> > > This was a common problem in the linux 2.4 series kernels, but has
> > > supposedly been fixed in the 2.6 kernels.  Having lots of memory and
> > > turning off swap will "fix" the problem in 2.4, but if you run out of
> > > real mem, you're hosed.
> > >
> > >
> > > ---------------------------(end of
broadcast)---------------------------
> > > TIP 4: Don't 'kill -9' the postmaster
> >
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster
>
>




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