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https://issues.apache.org/jira/browse/HIVE-1783?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12931328#action_12931328
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Namit Jain commented on HIVE-1783:
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Actually, on second thoughts, Siying, can you add more tests ?
set hive.join.emit.interval to a very small value (say 1), and add couple
of small data files to check all variants of join - single key followed by null
followed
by single key. Try to get the coverage on all those 'if' conditions
> CommonJoinOperator optimize the case of 1:1 join
> ------------------------------------------------
>
> Key: HIVE-1783
> URL: https://issues.apache.org/jira/browse/HIVE-1783
> Project: Hive
> Issue Type: Improvement
> Reporter: Siying Dong
> Assignee: Siying Dong
> Priority: Minor
> Attachments: HIVE-1783.1.patch
>
>
> CommonJoinOperator.genObject() is expensive. It does a recursive and keeps
> lots of states because it has to:
> 1. handle null cases for outer joins
> 2. handle the case of duplicated keys from one join party
> We can do a minor optimization to detect a 1:1 join (which is quite common)
> before calling CommonJoinOperator.genObject() and forward columns in a simple
> for-loop if we are sure neither of 1 or 2 will happen.
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