RE: how to tell if you are getting a partition wise join
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <ryan_gaffuri@xxxxxxxxxxx>
- Date: Thu, 20 Jul 2006 00:06:38 +0200
Ryan
>My expectation before running this query was:
>1. Each slave will scan a partition
>2. Then eight slaves will each do a partition wise hash join.
>3. The results will queued. The query coordinator will dequeue the results.
>
>Is this a correct interpretation?
Yes.
>I am not sure if the plan says that.
>
>This is the second plan:
> explain plan for
> select /*+ parallel (a,8) parallel (b,8) */ count(*)
> from hash_test_a partition(HASH_TEST_A01) a, hash_test_c
> partition(HASH_TEST_A01) b
> where a.object_id = b.object_id
A join is executed using a full partition-wise join if the partition row source
appears before the join row source. According to your attachment this is your
case. If you use, for example, 6 slaves, you should see a different execution
plan.
>I read the partition docs and it does not give examples of partition wise join
>explain plans.
AFAIK the Data Warehousing Guide describes partition wise joins quite well.
HTH
Chris
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