Re: Updated bitmap index patch

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Gavin Sherry <swm(at)alcove(dot)com(dot)au>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Updated bitmap index patch
Date: 2007-05-03 11:57:26
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Gavin Sherry wrote:
> Hi all,
> Attached is an updated bitmap index patch. It contains bug fixes, API
> changes, binary changes (page identifier to distinguish it from other
> indexes) and has been brought up to HEAD.
> I worked on a few approaches to VACUUM, none very satisfactory. The
> problem is, breaking a compressed word representing matches can have
> serious consequences -- at the least, creation of new words, at the worst,
> creation of a new page. If a lot of this were to happen, REINDEX would be
> much more efficient (this is what earlier patches did).
> One approach I looked at was modifying the existing read API to be able to
> do something like "kill prior tuple". This, I think, made the API quite
> complex and it was hard to implement, since the existing mechanism
> decompresses words on the fly and it would be hard to identify which TID
> is no longer a match. So, I dropped this idea pretty quickly.
> The second approach is to just manually traverse each vector and change
> matches to non-matches where necessary. The complexity then is in managing
> the consequences of breaking compressed words, doing WAL (efficiently) and
> calculating free space. I've only partially implemented this approach. At
> this stage, I don't have time to finish it due to other commitments.
> Thanks,
> Gavin

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Bruce Momjian <bruce(at)momjian(dot)us>

+ If your life is a hard drive, Christ can be your backup. +

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