Date: Thu, 13 Dec 2012 08:46:45 -0500
From: Bruce Momjian <bruce@momjian.us>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: 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: <20121213134645.GA15258@momjian.us>
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On Thu, Dec 13, 2012 at 09:40:40AM +0000, Simon Riggs wrote:
> On 13 December 2012 03:51, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> 
> >> Yes, this does seem like a problem for upgrades from 9.2 to 9.3?  We can
> >> have pg_dump --binary-upgrade set these, or have ANALYZE set it.   I
> >> would prefer the later.
> >
> > ANALYZE does not set that value, and is not going to start doing so,
> > because it doesn't scan enough of the table to derive a trustworthy
> > value.
> 
> ISTM that ANALYZE doesn't need to scan the table to do this. The
> vismap is now trustworthy and we can scan it separately on ANALYZE.
> 
> More to the point, since we run ANALYZE more frequently than we run
> VACUUM, the value stored by the last VACUUM could be very stale.

Wouldn't inserts affect the relallvisible ratio, but not cause a vacuum?
Seems we should be having analyze update this independent of pg_upgrade
needing it.  Also, why is this in pg_class?

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

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


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