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https://issues.apache.org/jira/browse/DRILL-7231?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gautam Parai updated DRILL-7231:
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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 the 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.
was:The join rowcount regresses a lot after changes made for DRILL-7148. This
affects several TPC-DS queries.
> TPCDS-21 regresses after fix for DRILL-7148
> -------------------------------------------
>
> Key: DRILL-7231
> URL: https://issues.apache.org/jira/browse/DRILL-7231
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Gautam Parai
> Assignee: Gautam Parai
> Priority: Major
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> The join rowcount regresses a lot after changes made for DRILL-7148. This
> affects several TPC-DS queries.
> One of the 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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