| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Josh berkus <josh(at)agliodbs(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Joe Conway <mail(at)joeconway(dot)com>, Victor Yegorov <vyegorov(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Reviewing freeze map code |
| Date: | 2016-05-18 22:43:48 |
| Message-ID: | 20160518224348.2psbzfen2xqros3a@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2016-05-18 18:42:16 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)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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