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https://issues.apache.org/jira/browse/HIVE-13149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15177892#comment-15177892
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Aihua Xu commented on HIVE-13149:
---------------------------------
Thanks [~szehon] to review the code.
1. get(Conf) and setConf(Conf) are almost the same, but get(Conf) will give you
an instance of Hive, but setConf(Conf) won't as. Of course get(Conf) can do
what setConf(Conf) does. I feel it's more clear. How do you think? I can remove
it if you don't feel the same.
2. MSC will get initialized when it's actually getting used. In many Task
threads, the tasks actually never need to access databases, but right now we
still open a connection to HMS.
> 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
>
>
> 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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