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Re: pg_basebackup blocking all queries with horrible performance

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Lonni J Friedman <netllama(at)gmail(dot)com>
Cc: Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>, Jerry Sievers <gsievers19(at)comcast(dot)net>, Magnus Hagander <magnus(at)hagander(dot)net>, pgsql-admin(at)postgresql(dot)org
Subject: Re: pg_basebackup blocking all queries with horrible performance
Date: 2012-06-09 06:53:35
Message-ID: CAOR=d=1vLOBPXcBhM+7kkUMFAb4oJpJREOxYqepHZX9o+ZyDuQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-hackers
On Fri, Jun 8, 2012 at 1:30 PM, Lonni J Friedman <netllama(at)gmail(dot)com> wrote:
> I've looked at iostat output both before & during pg_basebackup runs,
> and I'm not seeing any indication that the problem is due to disk IO
> bottlenecks.  The numbers don't vary very much at all between the good
> & bad times.  This is typical when pg_basebackup is running:
> ########
> Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s
> avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
> md0
>                  0.00     0.00   67.76   68.62     4.42     1.46
> 88.34     0.00    0.00    0.00    0.00   0.00   0.00
> ########
>
> and this is when the system is ok:
> ########
> Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s
> avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
> md0
>                  0.00     0.00   68.04   68.56     4.44     1.46
> 88.39     0.00    0.00    0.00    0.00   0.00   0.00
> ########

Two points.  1: md0 don't show things like %util, only the physical
drives will have that output, which is what you want to see, if it's
hopping up to 100%.  2: you need to run it with a number and get
something AFTER the first line, which is the average since the machine
was first turned on.

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