Date: Fri, 31 Jan 2014 22:22:07 -0500
From: Bruce Momjian <bruce@momjian.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@2ndquadrant.com>, Jim Nasby <jim@nasby.net>,
 Alvaro Herrera <alvherre@2ndquadrant.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
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On Thu, Sep 19, 2013 at 02:39:43PM -0400, Robert Haas 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.
> 
> Thoughts?  Let the hurling of rotten tomatoes begin.

Robert, where are we on this?  Should I post a patch?

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +


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