Re: Improvement of checkpoint IO scheduler for stable transaction responses

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Greg Smith <greg(at)2ndQuadrant(dot)com>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, KONDO Mitsumasa <kondo(dot)mitsumasa(at)lab(dot)ntt(dot)co(dot)jp>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Improvement of checkpoint IO scheduler for stable transaction responses
Date: 2013-07-18 19:40:24
Message-ID: 20130718194024.GR15510@tamriel.snowman.net
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* Greg Smith (greg(at)2ndQuadrant(dot)com) wrote:
> The first word that comes to mind for for just disregarding the end
> time is that it's a sloppy checkpoint. There is all sorts of sloppy
> behavior you might do here, but I've worked under the assumption
> that ignoring the contract with the administrator was frowned on by
> this project. If people want this sort of behavior in the server,
> I'm satisfied my distaste for the idea and the reasoning behind it
> is clear now.

For my part, I agree with Greg on this. While we might want to provide
an option of "go ahead and go past checkpoint timeout if the server gets
too busy to keep up", I don't think it should be the default.

To be honest, I'm also not convinced that this approach is better than
the existing mechanism where the user can adjust checkpoint_timeout to
be higher if they're ok with recovery taking longer and I share Greg's
concern about this backoff potentially running away and causing
checkpoints which never complete or do so far outside the configured
time.

Thanks,

Stephen

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