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https://issues.apache.org/jira/browse/HIVE-13149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15227466#comment-15227466
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Aihua Xu commented on HIVE-13149:
---------------------------------
[~ctang.ma] Agree that making copy of HiveConf is expensive so this patch will
save a lot of copies rather than adding copy of HiveConf. Currently each thread
will make a copy through {{Hive.get(new HiveConf(startSs.conf)).getMSC();}}. We
are removing that clone but just clone when necessary.
I don't see how ThreadLocal would help in here. Actually Hive.get(HiveConf) is
causing issue since the callers in many places are not cloning HiveConf and
get(HiveConf) probably is comparing HiveConf to itself.
I will evaluate the logic in the followup to simplify it though.
> 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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