From: | Neil Conway <neilc(at)samurai(dot)com> |
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To: | Kenneth Marshall <ktm(at)it(dot)is(dot)rice(dot)edu> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: left-deep plans? |
Date: | 2005-02-22 23:02:22 |
Message-ID: | 421BB9FE.5040908@samurai.com |
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Lists: | pgsql-hackers |
Kenneth Marshall wrote:
> GEQO is an attempt to provide a near-optimal join order without using
> an exhaustive search. "An exhaustive, deterministic search of a subset
> of the search space" has a non-zero probability of finding only a local
> minimum in execution time.
I'm not sure what you mean. By an "exhaustive, deterministic search of a
subset of the search space", I was referring to using the normal
planner, but restricting the search space to only left-deep plans. Since
GEQO will also only consider left-deep plans, ISTM there is no issue of
"local minima" that does not apply to an equal degree to GEQO itself.
> Since purely random selection, with learning, works so well, it may be
> worth developing a new random join-order optimization algorithm
Yeah, I agree. I've read a few papers on randomized algorithms for join
order selection, but none of them really seemed to be clear winners. Do
you have a reference for the paper you read?
-Neil
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