[ https://issues.apache.org/jira/browse/FLINK-15004?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16986719#comment-16986719 ]
Kurt Young commented on FLINK-15004: ------------------------------------ Is row count sufficient for us to decide whether we want to have one or two phase aggregation? I think the key's ndv will be much more important here. > Choose two-phase Aggregate 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 > Assignee: godfrey he > Priority: Major > Labels: pull-request-available > Fix For: 1.10.0 > > Time Spent: 10m > Remaining Estimate: 0h > > Currently, blink planner will use default rowCount value (defined in > {{FlinkPreparingTableBase#DEFAULT_ROWCOUNT}} ) when the statistics is > unknown, and maybe choose one-phase Aggregate. The job will hang if the data > is skewed. So It's better to use two-phase Aggregate for execution stability > if the statistics is unknown. -- This message was sent by Atlassian Jira (v8.3.4#803005)