Re: Eliminating VACUUM FULL WAS: remove flatfiles.c

From: Boszormenyi Zoltan <zb(at)cybertec(dot)at>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, daveg(at)sonic(dot)net, Andrew Dunstan <andrew(at)dunslane(dot)net>, Greg Stark <gsstark(at)mit(dot)edu>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Simon Riggs <simon(at)2ndQuadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Eliminating VACUUM FULL WAS: remove flatfiles.c
Date: 2009-09-04 19:01:27
Message-ID: 4AA16407.8050605@cybertec.at
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Tom Lane írta:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
>
>>>> I have a client who uses temp tables heavily, hundreds of thousands of
>>>> creates
>>>> and drops per day. They also have long running queries. The only
>>>> thing that
>>>> keeps catalog bloat somewhat in check is vacuum full on bloated catalogs
>>>> a few times a day. With
>>>>
>
>
>> Actually, this is a good point ... if we dropped VACUUM FULL, we'd need
>> to also be able to call CLUSTER (or VACUUM REWRITE) on the system catalogs.
>>
>
> I don't think I believe the claim above that vacuum full is actually
> necessary. Reasonably aggressive regular vacuuming ought to do it.
>

How about setting a non-100% fillfactor on catalog tables?
Maybe by default? That would also avoid most of the bloat, wouldn't it?

> We used to have a bug that caused row deletions during backend shutdown
> to not get reported to the stats collector; which had the effect that
> dead catalog entries for temp tables didn't get counted, and so autovac
> didn't hit the catalogs often enough, and so you'd get bloat in exactly
> this scenario. I suspect the claim that manual vacuum full is necessary
> is based on obsolete experience from before that bug got stomped.
> It's hardly an ideal solution anyway given what an exclusive lock on
> pg_class will do to the rest of the system --- and a cluster-like
> cleanup won't be any better about that.
>
> regards, tom lane
>
>

--
Bible has answers for everything. Proof:
"But let your communication be, Yea, yea; Nay, nay: for whatsoever is more
than these cometh of evil." (Matthew 5:37) - basics of digital technology.
"May your kingdom come" - superficial description of plate tectonics

----------------------------------
Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/

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