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https://issues.apache.org/jira/browse/FLINK-15004?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16985790#comment-16985790
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godfrey he commented on FLINK-15004:
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i would like to take this ticket
> Choose SortMergeJoin instead of HashJoin if the statistics is unknown
> ---------------------------------------------------------------------
>
> Key: FLINK-15004
> URL: https://issues.apache.org/jira/browse/FLINK-15004
> Project: Flink
> Issue Type: Sub-task
> Components: Table SQL / Planner
> Affects Versions: 1.9.0, 1.9.1
> Reporter: godfrey he
> Priority: Major
> Fix For: 1.10.0
>
>
> Currently, blink planner will use default rowCount value (defined in
> {{FlinkPreparingTableBase#DEFAULT_ROWCOUNT}} ) when the statistics is
> unknown, and maybe choose {{HashJoin}} instead of {{SortMergeJoin}}. The job
> will hang if the build side has huge input size. So It's better to use
> {{SortMergeJoin}} for execution stability if the statistics is unknown.
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