[jira] [Created] (FLINK-1267) Add crossGroup operator

["Fabian Hueske (JIRA)" <ji...@apache.org>]

Fabian Hueske created FLINK-1267:
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             Summary: Add crossGroup operator
                 Key: FLINK-1267
                 URL: https://issues.apache.org/jira/browse/FLINK-1267
             Project: Flink
          Issue Type: New Feature
          Components: Java API, Local Runtime, Optimizer, Scala API
    Affects Versions: 0.7.0-incubating
            Reporter: Fabian Hueske
            Priority: Minor


A common operator is to pair-wise compare or combine all elements of a group (there were two questions about this on the user mailing list, recently). Right now, this can be done in two ways:

1. {{groupReduce}}: consume and store the complete iterator in memory and build all pairs
2. do a self-{{Join}}: the engine builds all pairs of the full symmetric Cartesian product.

Both approaches have drawbacks. The {{groupReduce}} variant requires that the full group fits into memory and is more cumbersome to implement for the user, but pairs can be arbitrarily built. The self-{{Join}} approach pushes most of the work into the system, but the execution strategy does not treat the self-join different from a regular join (both identical inputs are shuffled, etc.) and always builds the full symmetric Cartesian product.

I propose to add a dedicated {{crossGroup()}} operator, that offers this functionality in a proper way.




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