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  1. Apache Drill
  2. DRILL-7231

TPCDS-21 regresses after fix for DRILL-7148

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: None
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      Description

      The join rowcount regresses a lot after changes made for DRILL-7148. This affects several TPC-DS queries.

      One of theĀ  fixes for DRILL-7148, introduced a change in DrillRelMDDistinctRowcount to only use the guess of 0.1*input_row_count when not all columns in the group-by key have NDV statistics. However, the fix was incorrect and instead caused it to use the guess-timate NDV even when statistics were present.

      Since the NDV was estimated as 0.1 * input_count_count because of the regression, the join cardinality was severely underestimated for TPCDS-21 = 400M * 15 / Max(400K, 15) = 150.

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              • Assignee:
                gparai Gautam Parai
                Reporter:
                gparai Gautam Parai
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