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Posted to issues@tajo.apache.org by "Jihoon Son (JIRA)" <ji...@apache.org> on 2015/08/16 09:07:45 UTC

[jira] [Created] (TAJO-1766) Improve the performance of cross join

Jihoon Son created TAJO-1766:
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             Summary: Improve the performance of cross join
                 Key: TAJO-1766
                 URL: https://issues.apache.org/jira/browse/TAJO-1766
             Project: Tajo
          Issue Type: Improvement
          Components: distributed query plan
            Reporter: Jihoon Son
            Assignee: Jihoon Son
             Fix For: 0.11.0


Cross join is one of the very heavy operations. Furthermore, this operator is performed by a single worker in the current implementation. (Please see the implementation of HashPartitioner. If partitionKeyIds is empty, getPartition() always returns a single value.)

One possible alternative is executing cross join with broadcast join. That is, outer table (smaller one) is always broadcasted, and join is performed by the machine who stores a part of inner table.

To do so, a new session variable is required to set the broadcast threshold for cross join. 



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