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https://issues.apache.org/jira/browse/HIVE-4470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13720392#comment-13720392
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Thejas M Nair commented on HIVE-4470:
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bq. Disallowing map joins on hive server 2 seems bad because of the performance
penalty.
By performance penalty, do you mean the increased latency because of MR job
launching? Yes, I agree this would be incurred. (Hopefully, the MR
framework/Tez improvements will bring that down.)
But on the other hand, if you have 10's or 100s of queries running
concurrently, having them run locally will potentially slow things down,
because of high resource utilization on HS2 machine. When we have something
like MR framework that does a good job of resource allocation, we should use
that.
That is why a config flag makes sense, so that admins can make this tradeoff.
bq. I can understand the argument for making the default off, but explicitly
disabling it is too extreme.
I did a poor job of describing what I meant. What I mean is this should be a
HS2 admin flag, that users who connect using jdbc should not be allowed to
override for their query. Admins themselves should be able to configure HS2 the
way they want.
> HS2 should disable local query execution
> ----------------------------------------
>
> Key: HIVE-4470
> URL: https://issues.apache.org/jira/browse/HIVE-4470
> Project: Hive
> Issue Type: Bug
> Components: HiveServer2
> Reporter: Thejas M Nair
>
> Hive can run queries in local mode (instead of using a cluster), if the size
> is small. This happens when "hive.exec.mode.local.auto" is set to true.
> This would affect the stability of the hive server2 node, if you have heavy
> query processing happening on it. Bugs in udfs triggered by a bad record can
> potentially add very heavy load making the server inaccessible.
> By default, HS2 should set these parameters to disallow local execution or
> send and error message if user tries to set these.
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