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.
I traced scanning of relation by editing the functions ReadBuffer()
and BufferAlloc(),StrategyGetBuffer().
That sounds valid.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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