From: Rudi Starcevic <tech@wildcash.com>
To: POSTGRES-PERFORMANCE <pgsql-performance@postgresql.org>
Subject: Re: slow queries, possibly disk io
Date: Mon, 30 May 2005 15:16:49 -0700
Message-ID: <429B90D1.9030402@wildcash.com> (raw)
In-Reply-To: <14584.1117204158@sss.pgh.pa.us>
References: <4a0cafe205052613242e0d4d10@mail.gmail.com>
<758d5e7f05052614232f6c9164@mail.gmail.com>
<4a0cafe205052706043ef8f53f@mail.gmail.com>
<4a0cafe205052706042d4e60e5@mail.gmail.com>
<14584.1117204158@sss.pgh.pa.us>
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.
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To: pgsql-performance@postgresql.org
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Subject: Re: slow queries, possibly disk io
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