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From "Nick Dimiduk (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SPARK-19609) Broadcast joins should pushdown join constraints as Filter to the larger relation
Date Wed, 15 Feb 2017 18:59:41 GMT
Nick Dimiduk created SPARK-19609:
------------------------------------

             Summary: Broadcast joins should pushdown join constraints as Filter to the larger
relation
                 Key: SPARK-19609
                 URL: https://issues.apache.org/jira/browse/SPARK-19609
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 2.1.0
            Reporter: Nick Dimiduk


For broadcast inner-joins, where the smaller relation is known to be small enough to materialize
on a worker, the set of values for all join columns is known and fits in memory. Spark should
translate these values into a {{Filter}} pushed down to the datasource. The common join condition
of equality, i.e. {{lhs.a == rhs.a}}, can be written as an {{a in ...}} clause. An example
of pushing such filters is already present in the form of {{IsNotNull}} filters via [~sameerag]'s
work on SPARK-12957 subtasks.

This optimization could even work when the smaller relation does not fit entirely in memory.
This could be done by partitioning the smaller relation into N pieces, applying this predicate
pushdown for each piece, and unioning the results.



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