Content-Type: text/plain; charset=UTF-8
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Florian Helmberger <fh@25th-floor.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [ADMIN] pg_class reltuples/relpages not updated by
	autovacuum/vacuum
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Kevin Grittner <kevin.grittner@wicourts.gov>
In-reply-to: <4DDCE9F4020000250003DC48@gw.wicourts.gov>
References: <4DD28F73.6010108@25th-floor.com> <25017.1306291669@sss.pgh.pa.us>
	<4DDCA801.70805@25th-floor.com> <19738.1306338472@sss.pgh.pa.us>
	<1306339028-sup-6948@alvh.no-ip.org>
	<22173.1306340636@sss.pgh.pa.us>
	<4DDCE9F4020000250003DC48@gw.wicourts.gov>
Date: Wed, 25 May 2011 12:55:09 -0400
Message-Id: <1306342228-sup-2964@alvh.no-ip.org>
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Excerpts from Kevin Grittner's message of mié may 25 12:37:24 -0400 2011:
> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>  
> > I don't know what client-side code might be looking at
> > relpages/reltuples.
>  
> I know that I find reltuples useful for getting an "accurate enough"
> sense of rows in a table (or set of tables) without resorting to
> count(*).  I'd be OK with any two of pages, tuples, and density; but
> dropping to one would make databases harder to manage, IMV.
>  
> Personally, I don't have much code that uses those columns;
> eliminating an existing column wouldn't involve much pain for me as
> long as it could still be derived.

Well, we only actually need to store one number, because you can figure
out a much more precise number-of-pages figure with pg_relation_size()
divided by configured page size.

(We feel free to hack around catalogs in other places, and we regularly
break pgAdmin and the like when we drop columns -- people just live with
it and update their tools.  I don't think it's such a big deal in this
particular case.)

-- 
Álvaro Herrera <alvherre@commandprompt.com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support