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https://issues.apache.org/jira/browse/HIVE-13149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15227197#comment-15227197
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Chaoyu Tang commented on HIVE-13149:
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Yeah, I also think the HiveConf copying is not necessary since Hive ql code
accesses HMS and performs actions via threadLocal Hive object which should
always be obtained via Hive.get(HiveConf). The Hive.get(HiveConf) already
compares the HiveConf to see if a new Hive and HiveMetaSStoreClient object
should be recreated. So I wonder if it is really necessary to cloning the conf
in each Hive, it seem quite expensive. But anyway it is to be removed in a
follow-up JIRA.
> 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, HIVE-13149.2.patch,
> HIVE-13149.3.patch, HIVE-13149.4.patch, HIVE-13149.5.patch,
> HIVE-13149.6.patch, HIVE-13149.7.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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