Thanx alot... its solved my problem On Mon, Aug 18, 2008 at 8:50 PM, Tom Lane <[EMAIL PROTECTED]> wrote:
> [ please keep the list cc'd for the archives' sake ] > > "Gauri Kanekar" <[EMAIL PROTECTED]> writes: > > On Mon, Aug 18, 2008 at 7:32 PM, Tom Lane <[EMAIL PROTECTED]> wrote: > >> No PG release since 7.3 would have voluntarily planned that query that > >> way. Maybe you were using join_collapse_limit = 1 to force the join > >> order? > > > Yes, We have set join_collapse_limit set to 1. > > Ah, so really your question is why join_collapse_limit isn't working as > you expect. That code changed quite a bit in 8.2, and the way it works > now is that the critical decision occurs while deciding whether to fold > the cross-join (a sub-problem of size 2) into the top-level join > problem. Which is a decision that's going to be driven by > from_collapse_limit not join_collapse_limit. > > So one way you could make it work is to reduce from_collapse_limit to > less than 3, but I suspect you'd find that that has too many bad > consequences for other queries. What's probably best is to write the > problem query like this: > > FROM table1 a cross join ( table2 b cross join table3 c ) > > which will cause join_collapse_limit to be the relevant number at both > steps. > > regards, tom lane > -- Regards Gauri
