On 24/08/11 17:22, Mark Kirkwood wrote:
On 24/08/11 15:15, Tom Lane wrote:
Hmmm ... this is structurally a pretty simple query, so I'm surprised
that 8.3 and 8.4 see it very much differently. The relation-level
estimates and plan choices are very nearly the same; the only thing
that's changed much is the estimates of the join sizes, and there were
not that many changes in the join selectivity estimation for simple
inner joins. I wonder whether you are seeing a bad side-effect of this
patch:
http://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=7f3eba30
Here is what the plan looks like with that patch reversed (it is back
to 8.3 speed too).
QUERY PLAN 8.4 - 7f3eba30 (better plan snipped)
I note from the commit message that the fix test case was from Grzegorz
Jaskiewicz (antijoin against a small subset of a relation). I was not
able to find this in the archives - Grzegorz do you recall the actual
test case? I thought it might be useful for me to spend some time
studying both cases and seeing if I can come up with any tweaks that
would let both your and my queries work well!
Cheers
Mark
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