Re: open items for 9.4

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, "David E(dot) Wheeler" <david(at)justatheory(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Jan Wieck <jan(at)wi3ck(dot)info>
Subject: Re: open items for 9.4
Date: 2014-09-29 20:41:45
Message-ID: 20140929204145.GG2084@awork2.anarazel.de
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On 2014-09-29 16:35:12 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On 2014-09-29 16:16:38 -0400, Tom Lane wrote:
> >> I wonder why it's a fixed constant at all, and not something like
> >> "wal_buffers / 8".
>
> > Because that'd be horrible performancewise on a system with many
> > wal_buffers. There's several operations where all locks are checked in
> > sequence (to see whether there's any stragglers that need to finish
> > inserting) and even some where they're acquired concurrently (e.g. for
> > xlog switch, checkpoint and such).
>
> Hm. Well, if there are countervailing considerations as to how large is a
> good value, that makes it even less likely that it's sensible to expose
> it as a user tunable.

Aren't there such considerations for most of the performance critical
gucs?

> A relevant analogy is that we don't expose a way
> to adjust the number of lock table partitions at runtime.

Which has worked out badly for e.g. the number of buffer partitions...

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

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