Re: [GENERAL] Rearranging simple where clauses

2011-05-05 Thread Igor Neyman
-Original Message- From: Michael Graham [mailto:mgra...@bloxx.com] Sent: Wednesday, May 04, 2011 11:59 AM To: pgsql-general@postgresql.org Subject: Re: Rearranging simple where clauses On Wed, 2011-05-04 at 11:49 -0400, Tom Lane wrote: > Well, you failed to show us any concrete examples

Re: [GENERAL] Rearranging simple where clauses

2011-05-04 Thread Michael Graham
On Wed, 2011-05-04 at 11:49 -0400, Tom Lane wrote: > Well, you failed to show us any concrete examples of the cases you > were looking at, but no I don't think the planner necessarily likes > "all the constants on one side". Most likely the win cases are where > one side of a WHERE-condition opera

Re: [GENERAL] Rearranging simple where clauses

2011-05-04 Thread Tom Lane
Michael Graham writes: > I did suspect that the answer would be that the difficulty out ways the > benefit. But in terms of driving the planner don't we always want to be > looking to move all the constants to one side of the expression since > the planner seems to like those? Well, you failed t

Re: [GENERAL] Rearranging simple where clauses

2011-05-04 Thread Michael Graham
On Wed, 2011-05-04 at 10:49 -0400, Tom Lane wrote: > Well, it'd require a very large amount of > type-specific/operator-specific knowledge, and it's not clear what > would drive the planner towards doing useful rearrangements rather > than counterproductive ones, and the number of real-world querie

Re: [GENERAL] Rearranging simple where clauses

2011-05-04 Thread Tom Lane
Michael Graham writes: > I was playing around with some sql in postgres and got to wondering why > the optimiser can't figure out that rearranging some expressions can > result in massive improvements in the queue plan. For example id + 5 < > 100 compared with id < 100 - 5. > Is it simply that n