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https://issues.apache.org/jira/browse/FLINK-15004?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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godfrey he updated FLINK-15004:
-------------------------------
    Description: 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 of {{HashJoin}} has huge input size. So It's better 
to use {{SortMergeJoin}} for execution stability if the statistics is unknown.  
(was: 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.)

> 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 of {{HashJoin}} has huge input size. So It's 
> better to use {{SortMergeJoin}} for execution stability if the statistics is 
> unknown.



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