To: "Steven Flatt" <steven.flatt@gmail.com>
cc: "Mark Kirkwood" <markir@paradise.net.nz>,
	"Gregory Stark" <stark@enterprisedb.com>,
	"Bill Moran" <wmoran@collaborativefusion.com>,
	"Vivek Khera" <vivek@khera.org>,
	"Pgsql performance" <pgsql-performance@postgresql.org>
Subject: Re: When/if to Reindex 
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Comments: In-reply-to "Steven Flatt" <steven.flatt@gmail.com>
	message dated "Fri, 24 Aug 2007 10:22:38 -0400"
Date: Fri, 24 Aug 2007 12:15:25 -0400
Message-ID: <1759.1187972125@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Steven Flatt" <steven.flatt@gmail.com> writes:
>> The fly in the ointment is that after collecting the pg_index definition
>> of the index, plancat.c also wants to know how big it is --- it calls
>> RelationGetNumberOfBlocks.

> Why do we even need to consider calling RelationGetNumberOfBlocks or looking
> at the pg_class.relpages entry?  My understanding of the expected behaviour
> is that while a reindex is happening, all queries run against the parent
> table are planned as though the index isn't there (i.e. it's unusable).

Where in the world did you get that idea?

If we had a REINDEX CONCURRENTLY it might work that way.  A normal
REINDEX cannot "mark" anything because it runs within a single
transaction; there is no way that it can emit any catalog changes
that will be visible before it's over.

			regards, tom lane