From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Reviewing freeze map code |
Date: | 2016-06-06 20:27:28 |
Message-ID: | 20160606202728.tomkrknleyvj5bbp@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2016-06-06 16:18:19 -0400, Stephen Frost wrote:
> That could be as simple as a query with the right things installed, or
> it might be an independent tool, but not having any way to check isn't
> good. That said, trying to make VACUUM do that doesn't make sense to me
> either.
The point is that VACUUM *has* these types of checks. And had so for
many years:
else if (all_visible_according_to_vm && !PageIsAllVisible(page)
&& VM_ALL_VISIBLE(onerel, blkno, &vmbuffer))
{
elog(WARNING, "page is not marked all-visible but visibility map bit is set in relation \"%s\" page %u",
relname, blkno);
visibilitymap_clear(onerel, blkno, vmbuffer);
}
...
else if (PageIsAllVisible(page) && has_dead_tuples)
{
elog(WARNING, "page containing dead tuples is marked as all-visible in relation \"%s\" page %u",
relname, blkno);
PageClearAllVisible(page);
MarkBufferDirty(buf);
visibilitymap_clear(onerel, blkno, vmbuffer);
}
the point is that, after the introduction of the freeze bit, there's no
way to reach them anymore (and they're missing a useful extension of
these warnings, but ...); these warnings have caught bugs. I don't
think it'd advocate for the vacuum option otherwise.
Greetings,
Andres Freund
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