From: Kevin Grittner <kgrittn@ymail.com>
To: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@2ndquadrant.com>
Cc: Jim Nasby <jim@nasby.net>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Peter Geoghegan <peter@2ndquadrant.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [PERFORM] encouraging index-only scans
Date: Thu, 19 Sep 2013 14:36:53 -0700 (PDT)
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Robert Haas <robertmhaas@gmail.com> wrote:
> Right now, whether or not to autovacuum is the rest of a two-pronged
> test. The first prong is based on number of updates and deletes
> relative to table size; that triggers a regular autovacuum. The
> second prong is based on age(relfrozenxid) and triggers a
> non-page-skipping vacuum (colloquially, an anti-wraparound vacuum).
>
> The typical case in which this doesn't work out well is when the table
> has a lot of inserts but few or no updates and deletes. So I propose
> that we change the first prong to count inserts as well as updates and
> deletes when deciding whether it needs to vacuum the table. We
> already use that calculation to decide whether to auto-analyze, so it
> wouldn't be very novel. We know that the work of marking pages
> all-visible will need to be done at some point, and doing it sooner
> will result in doing it in smaller batches, which seems generally
> good.
>
> However, I do have one concern: it might lead to excessive
> index-vacuuming. Right now, we skip the index vac step only if there
> ZERO dead tuples are found during the heap scan. Even one dead tuple
> (or line pointer) will cause an index vac cycle, which may easily be
> excessive. So I further propose that we introduce a threshold for
> index-vac; so that we only do index vac cycle if the number of dead
> tuples exceeds, say 0.1% of the table size.
+1 I've been thinking of suggesting something along the same lines,
for the same reasons.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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To: pgsql-performance@postgresql.org
Cc: kgrittn@ymail.com, robertmhaas@gmail.com, andres@2ndquadrant.com, jim@nasby.net, bruce@momjian.us, alvherre@2ndquadrant.com, peter@2ndquadrant.com, tgl@sss.pgh.pa.us, andrew@dunslane.net, pgsql-hackers@postgresql.org
Subject: Re: [PERFORM] encouraging index-only scans
In-Reply-To: <1379626613.94647.YahooMailNeo@web162901.mail.bf1.yahoo.com>
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