Subject: How long it takes to vacuum a big table
From: Csaba Nagy <nagy@ecircle-ag.com>
To: postgres performance list <pgsql-performance@postgresql.org>
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Message-Id: <1130512461.25950.20.camel@coppola.muc.ecircle.de>
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Date: Fri, 28 Oct 2005 17:14:21 +0200
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Hi all,

I wonder what is the main driving factor for vacuum's duration: the size
of the table, or the number of dead tuples it has to clean ?

We have a few big tables which are also heavily updated, and I couldn't
figure out a way to properly vacuum them. Vacuuming any of those took
very long amounts of time (I started one this morning and after ~5h30min
it's still running - and it's not even the biggest or most updated
table), which I can't really afford because it prevents other vacuum
processes on smaller tables to do their job due to the transaction open
for the long-running vacuum. 

BTW, is it in any way feasible to implement to make one vacuum not
blocking other vacuums from cleaning dead tuples after the first one
started ? I know it's the transaction not the vacuum which blocks, but
then wouldn't be a way to run vacuum somehow in "out of transaction
context" mode ?

Another issue: vacuum is not responding to cancel requests, at least not
in a reasonable amount of time...

Thanks in advance,
Csaba.