From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Manfred Koizar <mkoi-pg(at)aon(dot)at>, pgsql-patches(at)postgresql(dot)org, ohp(at)pyrenet(dot)fr, pgsql-hackers list <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [HACKERS] Index creation takes for ever |
Date: | 2003-09-07 16:25:12 |
Message-ID: | 200309071625.h87GPC810281@candle.pha.pa.us |
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Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Tom Lane wrote:
> >>> * Order duplicate index entries by tid for faster heap lookups
> >
> >> I don't know why that TODO entry exists, but I think the idea is
> >> counterproductive.
>
> > I assume you are talking about a unique index that probably only has a
> > few non-expired rows (in which case the newer rows first is better).
> > The TODO deals with cases where you have lots of valid duplicate index
> > rows, and you want to spin through all the matching rows in heap order
> > rather than randomly.
>
> Maybe so, but it would degrade the performance in the unique-index case
> if we do it as the TODO is worded.
Yes, the wording is just a guide.
> My own opinion is that the bitmap-index-lookup approach will be superior
> to trying to keep the index entries in TID order. (That's the idea
> we've been discussing for awhile of separating the heap-fetch stage from
> the index-scan stage: scan the index, make a sparse bitmap of the TIDs
> we need to visit, possibly AND or OR this bitmap with maps derived from
> other indexes, and finally visit the rows in heap order.)
Oh, yes.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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