Re: Query puts 7.3.4 on endless loop but 7.4beta5 is fine.

Tom Lane wrote:

Rajesh Kumar Mallah <mallah@trade-india.com> writes: 

SELECT DISTINCT main.* FROM
(  (     (        (           Tickets main  JOIN Groups as Groups_1  ON ( main.id = Groups_1.Instance)        )  JOIN        Principals as Principals_2  ON ( Groups_1.id = Principals_2.ObjectId)     ) JOIN     CachedGroupMembers as CachedGroupMembers_3  ON ( Principals_2.id = CachedGroupMembers_3.GroupId)  )  JOIN  Users as Users_4  ON ( CachedGroupMembers_3.MemberId = Users_4.id)
)   WHERE...   

I think the reason for the performance difference is that 7.3 treats
JOIN syntax as forcing a particular join order, while 7.4 doesn't.

Just out of curiosity , how does 7.4 determine the optimal Join Order?
is it GEQO in case of 7.4 although i did not enable it explicitly?
Thanks for the reply , I sent the EXPLAINs also just now.

What i really want is to help improving the Pg specific Component
for DBIx::SearchBuilder. The module is being widely used in
the  mod_perl world and has impact on the performance perception
of PostgreSQL.

		regards, tom lane