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Re: [PERFORM] Slow count(*) again...

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Andrew Dunstan <andrew(at)dunslane(dot)net>, Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>, "david(at)lang(dot)hm" <david(at)lang(dot)hm>, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Vitalii Tymchyshyn <tivv00(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: [PERFORM] Slow count(*) again...
Date: 2011-02-02 16:03:37
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Lists: pgsql-hackerspgsql-performance
Tom Lane wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> > On 02/01/2011 05:47 PM, Bruce Momjian wrote:
> >> Tom Lane wrote:
> >>> At this point what we've got is 25% of the runtime in nodeAgg.c overhead,
> >>> and it's difficult to see how to get any real improvement without tackling
> >>> that.
> >> Do we want a TODO about optimizing COUNT(*) to avoid aggregate
> >> processing overhead?
> > Whether or not it's bad application design, it's ubiquitous, and we 
> > should make it work as best we can, IMNSHO. This often generates 
> > complaints about Postgres, and if we really plan for world domination 
> > this needs to be part of it.
> I don't think that saving ~25% on COUNT(*) runtime will help that at all.
> The people who complain about it expect it to be instantaneous.
> If this sort of hack were free, I'd be all for doing it anyway; but I'm
> concerned that adding tests to enable a fast path will slow down every
> other aggregate, or else duplicate a lot of code that we'll then have to
> maintain.

OK, thank you.

  Bruce Momjian  <bruce(at)momjian(dot)us>

  + It's impossible for everything to be true. +

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