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https://issues.apache.org/jira/browse/HIVE-69?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12648800#action_12648800
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Raghotham Murthy commented on HIVE-69:
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ql/src/java/org/apache/hadoop/hive/ql/parse/GenMapRedTaskProcessor.java:128
As we discussed, this switch statement can be replaced with a more scalable
framework for rules. You would then have a tree pattern matcher (actually just
a path matcher initially) and a lookup for the associated transformer. With
this switch statement code structure, adding a new rule would either mean
writing a new visitor (duplicated code) or adding more cases to this switch
statement (resulting in huge functions).
> genMapRedTasks does not use the tree walker and uses implicit state which
> makes it difficult to enhance
> -------------------------------------------------------------------------------------------------------
>
> Key: HIVE-69
> URL: https://issues.apache.org/jira/browse/HIVE-69
> Project: Hadoop Hive
> Issue Type: Bug
> Reporter: Namit Jain
> Assignee: Namit Jain
>
> In SemanticAnalyzer, genmapredtasks() does not use a tree walker. For
> map-side joins, the taskplan needs to be enhanced to be possibly
> broken at MapSink also. Basically, the code is very difficult to enhance
> since there are implicit assumptions that reduce sink is the only
> operator where the plan breaks.
> This should be enhanced so that the user can implement their own task
> generation logic which is independent of the tree walking.
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