Tom Lane escreveu:
Gregory Stark <stark@xxxxxxxxxxxxxxxx> writes:
But I'm curious if you turn off mergejoin whether you can get a Nested Loop
plan and what cost 8.3 gives it. It looks to me like 8.3 came up with a higher
cost for Nested Loop than 8.1.9 (I think 8.1.10 came out with some planner
fixes btw) and so it's deciding these other plans are better. And they might
have been better for the imaginary scenario that the planner thinks is going
on.
Let me show this part again, to make things easier to understand =)
Nested Loop (cost=0.00..389461.65 rows=20000 width=38)
Total runtime: 22934.656 ms
Without hash and merge, the plan is exactly the same for 8.1 and 8.3.
No inicial cost for nested loops... it seems that hash < merge < nested
in this case.
Actually, now that I think about it, 8.3 should be *more* likely than
8.1 to choose a nestloop-with-inner-indexscan plan. 8.1 didn't have the
changes to allow a discount for repeated inner indexscans.
I'm wondering if
(a) the 8.1 installation being compared to had some planner cost
parameter changes that were not copied into the 8.3 installation; or
The parameters are at their default. The only changes made are in shared
buffers, work and maintenance mem.
(b) the only reason 8.1 likes the nestloop plan is that it has no
statistics on the test tables, whereas 8.3 does have stats because
of autovacuum being on by default.
I dont know if I understand what test tables you are talking about.
To run this tests I disabled autovacuum, and run "vacuum analyze test /
jtest" before.
--
[]´s,
André Volpato
Ecom Tecnologia LTDA - Análise e Desenvolvimento
andre.volpato@xxxxxxxxxxxxxxxxxxxxx
---------------------------(end of broadcast)---------------------------
TIP 1: if posting/reading through Usenet, please send an appropriate
subscribe-nomail command to majordomo@xxxxxxxxxxxxxx so that your
message can get through to the mailing list cleanly
