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

Tom Lane wrote:

>Rajesh Kumar Mallah <mallah(at)trade-india(dot)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
>
>