From: | Curt Sampson <cjs(at)cynic(dot)net> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | mark Kirkwood <markir(at)slithery(dot)org>, Gavin Sherry <swm(at)linuxworld(dot)com(dot)au>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: CLUSTER and indisclustered |
Date: | 2002-08-07 05:30:02 |
Message-ID: | Pine.NEB.4.44.0208071424440.1214-100000@angelic.cynic.net |
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Lists: | pgsql-hackers |
On Wed, 7 Aug 2002, Tom Lane wrote:
> But then you lose the possibility of combining multiple indexes through
> bitmap AND/OR steps, which seems quite interesting to me. If you've
> visited only a part of each index then you can't apply that concept.
Right. It'd be a shame to lose that, but a little is better than nothing
at all, if one ends up being faced with that decision.
> Another point to keep in mind is that the bigger the bitmap gets, the
> less useful an indexscan is, by definition --- sooner or later you might
> as well fall back to a seqscan.
Well, yes, so long as you chose the correct values of "big." I'd want
this to be able to optimize queries against a two billion row table
about 150 GB in size. And that might even get bigger in a few years.
> Maybe this seems natural
> to me as an old JPEG campaigner, but if you don't see the logic I
> recommend thinking about it a little ...
Well, photos are certainly not random, but database tables may be
in essentially random order far more often. How much that applies,
I'm not sure, since I don't really know a lot about this stuff.
I'll take your word for it on what's best there.
cjs
--
Curt Sampson <cjs(at)cynic(dot)net> +81 90 7737 2974 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC
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