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Re: A bunch of minor issues

From: Dave Page <dpage(at)postgresql(dot)org>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: pgadmin-hackers(at)postgresql(dot)org, Guillaume Lelarge <guillaume(at)lelarge(dot)info>
Subject: Re: A bunch of minor issues
Date: 2007-09-26 13:21:18
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgadmin-hackers
Heikki Linnakangas wrote:
> Dave Page wrote:
>> REINDEX is similar to a drop and recreate of the index in that the index
>> contents are rebuilt from scratch. However, the locking considerations
>> are rather different. REINDEX locks out writes but not reads of the
>> index's parent table. It also takes an exclusive lock on the specific
>> index being processed, which will block reads that attempt to use that
>> index. In contrast, DROP INDEX momentarily takes exclusive lock on the
>> parent table, blocking both writes and reads. The subsequent CREATE
>> INDEX locks out writes but not reads; since the index is not there, no
>> read will attempt to use it, meaning that there will be no blocking but
>> reads may be forced into expensive sequential scans. Another important
>> point is that the drop/create approach invalidates any cached query
>> plans that use the index, while REINDEX does not.
> So the advantage is that drop+create will allow all reads to run
> concurrently, though they might have to use sequential scans. Hmm, I
> wonder if a CREATE+DROP+rename would be even better. Could use
> CONCURRENT-mode in the create as well to allow concurrent writes...

Would be even nicer to include in the server... maybe REINDEX 

> I know I know, no new features at this point :).

Indeed :-)


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