[jira] [Commented] (SPARK-9258) Remove all semi join physical operator

["Reynold Xin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-9258?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660579#comment-14660579 ] 

Reynold Xin commented on SPARK-9258:
------------------------------------

Marking as won't fix for now. We cannot replace semi join with normal join, because the semantics are different. However, we can reuse the same join maps for the hashsets.


> Remove all semi join physical operator
> --------------------------------------
>
>                 Key: SPARK-9258
>                 URL: https://issues.apache.org/jira/browse/SPARK-9258
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Reynold Xin
>
> We have 4 semi join operators. In this case, they are not very very necessary. We can still use an equi-join operator to do the join, and just not include any values from the other join.
> We waste a little bit space due to building a hash map rather than a hash set, but at the end of the day unless we are going to spend a lot of time optimizing hash set, our Tungsten hash map will be a lot more efficient than the hash set anyway. This way, semi-join automatically benefits from all the work we do in Tungsten.



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