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  1. IMPALA
  2. IMPALA-5120

Consider defaulting to partitioned join when no stats are available.

    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Critical
    • Resolution: Fixed
    • Affects Version/s: Impala 2.9.0
    • Fix Version/s: Impala 2.9.0
    • Component/s: Frontend
    • Labels:
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      Description

      We currently default to broadcast join when no stats are available, since the code estimates are both MAX_LONG and in the case of equal costs, broadcast wins. We should consider making partitioned join the default because it will use less memory.

      The code is here: https://github.com/apache/incubator-impala/blob/master/fe/src/main/java/org/apache/impala/planner/DistributedPlanner.java#L509

          && (node.getDistributionModeHint() == DistributionMode.BROADCAST
                  || (node.getDistributionModeHint() != DistributionMode.PARTITIONED
      && broadcastCost <= partitionCost)))
      

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              • Assignee:
                twmarshall Thomas Tauber-Marshall
                Reporter:
                tarmstrong Tim Armstrong
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                  Updated:
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