Greg Hogan created FLINK-3910:
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Summary: New self-join operator
Key: FLINK-3910
URL: https://issues.apache.org/jira/browse/FLINK-3910
Project: Flink
Issue Type: New Feature
Components: DataSet API, Java API, Scala API
Affects Versions: 1.1.0
Reporter: Greg Hogan
Assignee: Greg Hogan
Flink currently provides inner- and outer-joins as well as cogroup and the
non-keyed cross. {{JoinOperator}} hints at future support for semi- and
anti-joins.
Many Gelly algorithms perform a self-join [0]. Still pending reviews,
FLINK-3768 performs a self-join on non-skewed data in TriangleListing.java and
FLINK-3780 performs a self-join on skewed data in JaccardSimilarity.java. A
{{SelfJoinHint}} will select between skewed and non-skewed implementations.
The object-reuse-disabled case can be simply handled with a new {{Operator}}.
The object-reuse-enabled case requires either {{CopyableValue}} types (as in
the code above) or a custom driver which has access to the serializer (or
making the serializer accessible to rich functions, and I think there be
dragons).
If the idea of a self-join is agreeable, I'd like to work out a rough
implementation and go from there.
[0] https://en.wikipedia.org/wiki/Join_%28SQL%29#Self-join
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