From: Josh Close <narshe@gmail.com>
To: POSTGRES-PERFORMANCE <pgsql-performance@postgresql.org>
Subject: Re: slow queries, possibly disk io
Date: Tue, 31 May 2005 08:17:31 -0500
Message-ID: <4a0cafe20505310617d803a0c@mail.gmail.com> (raw)
In-Reply-To: <429B90D1.9030402@wildcash.com>
References: <4a0cafe205052613242e0d4d10@mail.gmail.com>
<758d5e7f05052614232f6c9164@mail.gmail.com>
<4a0cafe205052706043ef8f53f@mail.gmail.com>
<4a0cafe205052706042d4e60e5@mail.gmail.com>
<14584.1117204158@sss.pgh.pa.us>
<429B90D1.9030402@wildcash.com>
I didn't see iostat as available to install, but I'm using dstat to see this.
The server has constant disk reads averaging around 50M and quite a
few in the 60M range. This is when selects are being done, which is
almost always. I would think if postgres is grabbing everything from
memory that this wouldn't happen. This is why I think there must be
some way to allocate more mem to postgres.
There is 2 gigs of mem in this server. Here are my current settings.
max_connections = 100
shared_buffers = 50000
sort_mem = 4096
vacuum_mem = 32768
effective_cache_size = 450000
Shared buffers is set to 10% of total mem. Effective cache size is 90% of mem.
Is there anything that can be done to have postgres grab more from
memory rather than disk?
On 5/30/05, Rudi Starcevic <tech@wildcash.com> wrote:
> Hi,
>
> I had some disk io issues recently with NFS, I found the command 'iostat
> -x 5' to be a great help when using Linux.
>
> For example here is the output when I do a 10GB file transfer onto hdc
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
> avgrq-sz avgqu-sz await svctm %util
> hdc 0.00 875.95 0.00 29.66 0.00 7244.89 0.00 3622.44
> 244.27 3.07 103.52 1.78 5.27
>
> The last field show the disk is 5.27% busy.
>
> I have seen this value at 100%, adding more server brought it under 100%.
> It seems that if you hit 100% problems sort of cascade all over that
> place. For example Apache connections went right up and hit their max.
>
> I am not sure how accurate the % is but it has work pretty well for me.
>
> Perhaps use this command in another window with you run your SQL and see
> what it shows.
>
> HTH.
> Kind regards,
> Rudi.
>
> ---------------------------(end of broadcast)---------------------------
> TIP 7: don't forget to increase your free space map settings
>
--
-Josh
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Subject: Re: slow queries, possibly disk io
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