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https://issues.apache.org/jira/browse/HIVE-13149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15169492#comment-15169492
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Aihua Xu commented on HIVE-13149:
---------------------------------
That's is about performance. We actually can share one HMS connection in
extreme in one HS2 but sharing the connection will cause the one HMS execution
to wait for the other long HMS execution.
> Remove some unnecessary HMS connections from HS2
> -------------------------------------------------
>
> Key: HIVE-13149
> URL: https://issues.apache.org/jira/browse/HIVE-13149
> Project: Hive
> Issue Type: Sub-task
> Components: HiveServer2
> Affects Versions: 2.0.0
> Reporter: Aihua Xu
> Assignee: Aihua Xu
> Attachments: HIVE-13149.1.patch
>
>
> In SessionState class, currently we will always try to get a HMS connection
> in {{start(SessionState startSs, boolean isAsync, LogHelper console)}}
> regardless of if the connection will be used later or not.
> When SessionState is accessed by the tasks in TaskRunner.java, although most
> of the tasks other than some like StatsTask, don't need to access HMS.
> Currently a new HMS connection will be established for each Task thread. If
> HiveServer2 is configured to run in parallel and the query involves many
> tasks, then the connections are created but unused.
> {noformat}
> @Override
> public void run() {
> runner = Thread.currentThread();
> try {
> OperationLog.setCurrentOperationLog(operationLog);
> SessionState.start(ss);
> runSequential();
> {noformat}
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