Nick Dimiduk created SPARK-19609:
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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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