To: "Steve Oualline" <soualline@stbernard.com>
cc: pgsql-performance@postgresql.org, "Jiu Zheng" <Jiu@stbernard.com>
Subject: Re: VACUUM Performance 
In-reply-to: <00C5463E8A5F7C41A8396D701A6734B1527A62@mail01.stbernard.com> 
References: <00C5463E8A5F7C41A8396D701A6734B1527A62@mail01.stbernard.com>
Comments: In-reply-to "Steve Oualline" <soualline@stbernard.com>
	message dated "Fri, 20 Oct 2006 14:42:30 -0700"
Date: Sat, 21 Oct 2006 01:02:06 -0400
Message-ID: <21641.1161406926@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Steve Oualline" <soualline@stbernard.com> writes:
> Question:   I have a big table with 120,000,000 records.
> Let's assume that I DELETE 4,000,000 records, VACUUM FULL, and REINDEX.
> Now I have the same table, but with 240,000,000 records.
> I DELETE 8,000,000 records, VACUUM FULL, and REINDEX.
> Should the second operation with twice the data take twice the time as =
> the first?

At least.  If you intend to reindex all the indexes, consider instead
doing
	DROP INDEX(es)
	VACUUM FULL
	re-create indexes
as this avoids the very large amount of effort that VACUUM FULL puts
into index maintenance --- effort that's utterly wasted if you then
reindex.

CLUSTER and some forms of ALTER TABLE can accomplish a table rewrite
with less hassle than the above, although strictly speaking they violate
MVCC by discarding recently-dead tuples.

			regards, tom lane