[jira] [Resolved] (SPARK-20881) Clearly document the mechanism to choose between two sources of statistics

["Xiao Li (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-20881?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Xiao Li resolved SPARK-20881.
-----------------------------
       Resolution: Fixed
         Assignee: Zhenhua Wang
    Fix Version/s: 2.3.0

> Clearly document the mechanism to choose between two sources of statistics
> --------------------------------------------------------------------------
>
>                 Key: SPARK-20881
>                 URL: https://issues.apache.org/jira/browse/SPARK-20881
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 2.2.0
>            Reporter: Zhenhua Wang
>            Assignee: Zhenhua Wang
>             Fix For: 2.3.0
>
>
> Currently in Spark, statistics are generated by "analyze" commands. 
> When user updates the table and collects stats in Hive, "totalSize"/"numRows" will be updated in metastore. 
> Then, in spark side, table stats becomes stale and is different from Hive's stats. 
> This is expected. Currently, we have two sources of statistics, i.e. Spark's stats and Hive's stats. In our design, once Spark's stats is available, we respect it over Hive's stats.
> If a user generated stats at Spark side, it's his responsibility to update Spark's stats by re-running analyze commands.
> But we should clearly document in related code the mechanism to choose between these two sources of stats.



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