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Re: is pg_autovacuum so effective ?

From: Christopher Browne <cbbrowne(at)ca(dot)afilias(dot)info>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: is pg_autovacuum so effective ?
Date: 2005-02-23 05:31:58
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Gaetano Mendola <mendola(at)bigfoot(dot)com> writes:

> Tom Lane wrote:
>> Gaetano Mendola <mendola(at)bigfoot(dot)com> writes:
>>>I'm using ony pg_autovacuum. I expect that disk usage will reach
>>>a steady state but is not. PG engine: 7.4.5
>> One data point doesn't prove that you're not at a steady state.
> I do a graph about my disk usage and it's a ramp since one week,
> I'll continue to wait in order to see if it will decrease.
> I was expecting the steady state at something like 4 GB
> ( after a full vacuum and reindex ) + 10 % = 4.4 GB
> I'm at 4.6 GB and increasing. I'll see how it will continue.

You probably want for the "experiment" to last more than a week.

After all, it might actually be that with your usage patterns, that
table would stabilize at 15% "overhead," and that might take a couple
or three weeks.

Unless it's clear that it's growing perilously quickly, just leave it
alone so that there's actually some possibility of reaching an
equilibrium.  Any time you "VACUUM FULL" it, that _destroys_ any
experimental results or any noticeable patterns, and it guarantees
that you'll see "seemingly perilous growth" for a while.

And if the table is _TRULY_ growing "perilously quickly," then it is
likely that you should add in some scheduled vacuums on the table.
Not VACUUM FULLs; just plain VACUUMs.

I revised cron scripts yet again today to do hourly and "4x/day"
vacuums of certain tables in some of our systems where we know they
need the attention.  I didn't schedule any VACUUM FULLs; it's
unnecessary, and would lead directly to system outages, which is
totally unacceptable.
Christopher Browne
(416) 673-4124 (land)

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