Date: Fri, 6 Sep 2013 15:08:54 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Bruce Momjian <bruce@momjian.us>, Robert Haas <robertmhaas@gmail.com>,
 Peter Geoghegan <peter@2ndquadrant.com>,
 Tom Lane <tgl@sss.pgh.pa.us>, Andrew Dunstan <andrew@dunslane.net>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [PERFORM] encouraging index-only scans
Message-ID: <20130906130854.GB600952@alap2.anarazel.de>
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On 2013-09-06 01:22:36 -0400, Alvaro Herrera wrote:
> I think it's shortsighted to keep thinking of autovacuum as just a way
> to run VACUUM and ANALYZE.  We have already discussed work items that
> need to be done separately, such as truncating the last few empty pages
> on a relation that was vacuumed recently.  We also need to process a GIN
> index' pending insertion list; and with minmax indexes I will want to
> run summarization of heap page ranges.

Agreed.

> So maybe instead of trying to think of VM bit setting as part of vacuum,
> we could just keep stats about how many pages we might need to scan
> because of possibly needing to set the bit, and then doing that in
> autovacuum, independently from actually vacuuming the relation.

I am not sure I understand this though. What would be the point to go
and set all visible and not do the rest of the vacuuming work?

I think triggering vacuuming by scanning the visibility map for the
number of unset bits and use that as another trigger is a good idea. The
vm should ensure we're not doing superflous work.

Greetings,

Andres Freund

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


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