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Posted to dev@flink.apache.org by "Caizhi Weng (Jira)" <ji...@apache.org> on 2020/10/23 08:07:00 UTC

[jira] [Created] (FLINK-19780) FlinkRelMdDistinctRowCount#getDistinctRowCount(Calc) will always return 0 when number of rows are large

Caizhi Weng created FLINK-19780:
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             Summary: FlinkRelMdDistinctRowCount#getDistinctRowCount(Calc) will always return 0 when number of rows are large
                 Key: FLINK-19780
                 URL: https://issues.apache.org/jira/browse/FLINK-19780
             Project: Flink
          Issue Type: Bug
          Components: Table SQL / Planner
            Reporter: Caizhi Weng
             Fix For: 1.12.0


Due to CALCITE-4351 {{FlinkRelMdDistinctRowCount#getDistinctRowCount(Calc)}} will always return 0 when number of rows are large.

What I would suggest is to introduce our own {{FlinkRelMdUtil#numDistinctVals}} to treat small and large inputs in different ways. For small inputs we use the more precise {{RelMdUtil#numDistinctVals}} and for large inputs we copy the old, approximated implementation of {{RelMdUtil#numDistinctVals}}.

This is a temporary solution. When CALCITE-4351 is fixed we should revert this commit.



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