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@cynic.net> +81 90 7737 2974 http://www.netbsd.org Don't you know, in this new Dark Age, we're
alllight. --XTC
