Re: UPDATEDs slowing SELECTs in a fully cached database

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: <pgsql-performance(at)postgresql(dot)org>, "Craig Ringer" <craig(at)postnewspapers(dot)com(dot)au>, "lars hofhansl" <lhofhansl(at)yahoo(dot)com>
Subject: Re: UPDATEDs slowing SELECTs in a fully cached database
Date: 2011-07-11 17:33:47
Message-ID: 4E1AEDAB020000250003F1C3@gw.wicourts.gov
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lars hofhansl <lhofhansl(at)yahoo(dot)com> wrote:

> Yep, I am not seeing the SELECTs slow down (measurably) during
> checkpoints (i.e. when dirty pages are flushed to disk), but only
> during writing of the WAL files.

How about if you do a whole slew of the UPDATEs and then stop those
and run a bunch of SELECTs? (I don't think I've seen anything
mentioned so far which rules out hint bit rewrites as an issue.)

I see you have tweaked things to balance the writes -- you might
want to try further adjustments to reduce backend writes and see
what happens.

-Kevin

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