Re: 8.4 optimization regression? - Mailing list pgsql-performance

From Tom Lane
Subject Re: 8.4 optimization regression?
Date
Msg-id 26940.1314918836@sss.pgh.pa.us
Whole thread Raw
In response to Re: 8.4 optimization regression?  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: 8.4 optimization regression?  (Mark Kirkwood <mark.kirkwood@catalyst.net.nz>)
List pgsql-performance
I wrote:
> Mark Kirkwood <mark.kirkwood@catalyst.net.nz> writes:
>> [ assorted examples showing that commit
>> 7f3eba30c9d622d1981b1368f2d79ba0999cdff2 has got problems ]

> ...
> So, not only are you correct that we should revert the changes to
> eqjoinsel_inner, but what's happening in eqjoinsel_semi is wrong too.

I've retested these examples with the patches I committed yesterday.
Six of the eight examples are estimated pretty nearly dead on, while the
other two are estimated about 50% too high (still a lot better than
before).  AFAICT there's no easy way to improve those estimates further;
eqjoinsel_semi just plain hasn't got enough information to know how many
matches there will be.

            regards, tom lane

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