| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Pål Stenslet <paal(dot)stenslet(at)exie(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Should Oracle outperform PostgreSQL on a complex |
| Date: | 2005-12-18 17:53:27 |
| Message-ID: | 1134928407.2964.177.camel@localhost.localdomain |
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| Lists: | pgsql-performance |
On Sun, 2005-12-18 at 17:07 +1300, Mark Kirkwood wrote:
> Tom Lane wrote:
>
> >>2. transform joins into subselects, then return subselect rows via an
> >>index bitmap. Joins are performed via a bitmap addition process.
>
> Looks like 8.1 pretty much does this right now:
Good analysis.
8.1 doesn't do:
- the transforms sufficiently well (you just performed them manually)
- doesn't AND together multiple bitmaps to assist with N-way joins
Those aren't criticisms, just observations. Pal's original example was a
9-dimension join, so I think PostgreSQL does very well on making that
run in 30 seconds. That's a complex example and I think upholds just how
good things are right now.
Anyway, back to the starting point: IMHO there is an additional
optimisation that can be performed to somehow speed up Single large
table-many small table joins. And we have some clues as to how we might
do that.
Best Regards, Simon Riggs
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