Re: [GENERAL] Hash join in 8.3

[André Volpato]

Tom Lane escreveu: Gregory Stark <[EMAIL PROTECTED]> 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. 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 (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. regards, tom lane I think I found the answer! 8.1: likes nested loop even after vacuumdb on the database. 8.3: likes hash at first time but: - after vacuumdb *on the database* (I was running on the tables.....), it turns out to:  Merge Join  (cost=178779.93..328503.44 rows=30000 width=38) in 20005.207 ms #set enable_mergejoin=off;  Hash Join  (cost=156644.00..365204.03 rows=30000 width=38) in 29104.390 ms  * a very faster hash here, seqscanning the smaller table before the bigger one. Tricky! I wont trust table vacuums anymore... -- []´s, André Volpato Ecom Tecnologia LTDA - Análise e Desenvolvimento [EMAIL PROTECTED]