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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Josh berkus <josh@agliodbs.com>
Cc: Peter Geoghegan <pg@heroku.com>
Cc: Jeff Janes <jeff.janes@gmail.com>
Cc: Joe Conway <mail@joeconway.com>
Cc: Victor Yegorov <vyegorov@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Reviewing freeze map code
Date: Wed, 18 May 2016 15:43:48 -0700
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On 2016-05-18 18:42:16 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > On 2016-05-18 18:25:39 -0400, Tom Lane wrote:
> >> Yes, I've been wondering that too.  VACUUM is not meant as a corruption
> >> checker, and should not be made into one, so what is the point of this
> >> flag exactly?
> 
> > Well, so far a VACUUM FREEZE (or just setting vacuum_freeze_table_age =
> > 0) verified the correctness of the visibility map; and that found a
> > number of bugs.  Now visibilitymap grew additional responsibilities,
> > with a noticeable risk of data eating bugs, and there's no way to verify
> > whether visibilitymap's frozen bits are set correctly.
> 
> Meh.  I'm not sure we should grow a rather half-baked feature we'll never
> be able to remove as a substitute for a separate sanity checker.  The
> latter is really the right place for this kind of thing.

It's not a new feature, it's a feature we removed as a side effect. And
one that allows us to evaluate whether the new feature actually works.


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