From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Josh berkus <josh@agliodbs.com>, Peter Geoghegan <pg@heroku.com>,
        Jeff Janes <jeff.janes@gmail.com>, Joe Conway <mail@joeconway.com>,
        Victor Yegorov <vyegorov@gmail.com>,
        Robert Haas <robertmhaas@gmail.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Reviewing freeze map code
In-reply-to: <20160518223436.w32fzgoui6gaaj4p@alap3.anarazel.de>
References: 
 <CA+TgmobZNDJGvKOM=qLzXqwZUdqowPKvG3gcp5WAMiypezOhig@mail.gmail.com>
 <573C714D.2060505@commandprompt.com>
 <CA+TgmoYE6wCKpoxnoJfqizpi-zTYHvjgN0YWR-hPzbZDWR_m6w@mail.gmail.com>
 <CAGnEboiRvMQeyHW4RqtY8Lb4vVTT6hKg_eCEnM=J+yXm3sETVQ@mail.gmail.com>
 <573C77AF.8030201@joeconway.com>
 <CAMkU=1ygHztvjr-hS3RRLyYmEdZkTDrwf5Cjch4xa5HLcpZRDQ@mail.gmail.com>
 <CAM3SWZQqqrA+EGaandmr9bOHM1-pcuDs3Ey5HDLCFc0C_4DCYw@mail.gmail.com>
 <WM!c3a6cf0190f9c5d6f5a9a6310a38bac5c64c41d23fe8f04f9856771643267f4ec3291c98a2074de25420aae13297044e!@asav-3.01.com>
 <573CCB9C.50705@agliodbs.com> <15044.1463610339@sss.pgh.pa.us>
 <20160518223436.w32fzgoui6gaaj4p@alap3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Wed, 18 May 2016 15:34:36 -0700"
Date: Wed, 18 May 2016 18:42:16 -0400
Message-ID: <15161.1463611336@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

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.

			regards, tom lane


-- 
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers