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https://issues.apache.org/jira/browse/HIVE-9223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14277829#comment-14277829
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Vikram Dixit K commented on HIVE-9223:
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[~pala] I see how this can happen now. In tez only one DAG is allowed to run at
a time. MR subverts this issue by just launching multiple jobs when such a
parallel submission is done. However, this change is not easy to do in case of
tez right now and we need to have a design to support concurrency at this
level. I am exploring some options with the tez folks and will get back to you
on this.
> HiveServer2 on Tez doesn't support concurrent queries within one session
> ------------------------------------------------------------------------
>
> Key: HIVE-9223
> URL: https://issues.apache.org/jira/browse/HIVE-9223
> Project: Hive
> Issue Type: Bug
> Components: HiveServer2
> Reporter: Pala M Muthaia
>
> When a user submits multiple queries in the same HS2 session (using thrift
> interface) concurrently, the query goes through the same TezSessionState and
> ends up being submitted to the same Tez AM, and the second query fails with
> the error "App master already running a DAG"
> Is this by design? I looked into the code, and the comments as well as the
> code suggest support only for serial execution of queries within the same
> HiveServer2 session (on tez).
> This works for CLI environment but in a server, it is plausible that client
> sends multiple concurrent queries under the same session (e.g: a web app that
> executes queries for user, such as Cloudera Hue). So shouldn't HS2 on Tez
> implementation support concurrent queries?
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