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  1. Hive
  2. HIVE-1772

optimize join followed by a groupby

    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Major
    • Resolution: Not A Problem
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: Query Processor
    • Labels:
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      Description

      explain SELECT x.key, count(1) FROM src1 x JOIN src y ON (x.key = y.key) group by x.key;

      STAGE DEPENDENCIES:
      Stage-1 is a root stage
      Stage-2 depends on stages: Stage-1
      Stage-0 is a root stage

      The above query issues 2 map-reduce jobs.
      The first MR job performs the join, whereas the second MR performs the group by.
      Since the data is already sorted, the group by can be performed in the reducer of the join itself.

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              • Assignee:
                Unassigned
                Reporter:
                namit Namit Jain
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                • Created:
                  Updated:
                  Resolved: