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https://issues.apache.org/jira/browse/SPARK-21083?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zhenhua Wang updated SPARK-21083:
---------------------------------
    Description: 
Suppose we already collected column stats for some columns before, then, when 
we collect column stats for other columns:
* If the table is changed during two collecting actions, we need to remove 
these stale column stats, only keep the latest stats.
* Otherwise, combine these two sets of column stats.

Note that we always update sizeInBytes/rowCount when collecting column stats, 
that logic doesn't need change.

  was:
Suppose we already collected column stats for some columns before, then, when 
we collect column stats for other columns:
* If the table is changed during two collecting actions, we need to remove 
these stale column stats, only keep the latest stats.
* Otherwise, combine these two sets of column stats.
* 
Note that we always update sizeInBytes/rowCount when collecting column stats, 
that logic doesn't need change.


> Consider staleness when collecting column stats
> -----------------------------------------------
>
>                 Key: SPARK-21083
>                 URL: https://issues.apache.org/jira/browse/SPARK-21083
>             Project: Spark
>          Issue Type: Sub-task
>          Components: SQL
>    Affects Versions: 2.3.0
>            Reporter: Zhenhua Wang
>
> Suppose we already collected column stats for some columns before, then, when 
> we collect column stats for other columns:
> * If the table is changed during two collecting actions, we need to remove 
> these stale column stats, only keep the latest stats.
> * Otherwise, combine these two sets of column stats.
> Note that we always update sizeInBytes/rowCount when collecting column stats, 
> that logic doesn't need change.



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