Heikki Linnakangas wrote: > Praveen Kumar N wrote: > >Let me explain once more. > > > >I have two relations which are 10 times more than bufferpool size.I > >have observed the following things when joined that two relations(it > >using merge join to join both relations) > > > >1.It first accessed system catalog tables > >2.Relation 1 > >3.Relation 2 > > > >my doubt is one whole relation cant fit in the main memory.That too > >when we use merge join, it should keep some part of 1st relations and > >should scan second relation as bufferpool size is less compared to > >size of each relation.similarly for the remainin part of 1st > >relation.But it is not happening here.First whole Relation1 is scanned > >and then Relation 2 is scanned. Then how is it joining two relations > >using merge join? Am I missing something? > > Hmm. A hash join, maybe? You should do EXPLAIN on the query to see what > it really does, otherwise we're just guessing.
Another option would be that the tuples are written to a sort tape, I think. -- Alvaro Herrera http://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support ---------------------------(end of broadcast)--------------------------- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
