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https://issues.apache.org/jira/browse/IMPALA-7802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16710806#comment-16710806
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Tim Armstrong commented on IMPALA-7802:
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[~zoram] The thing is does do is report a meaningful error message when the
user comes back and tries to use the session - i.e. "Client session expired due
to more than...".
E.g. a quick google revealed this forum thread where the error message pointed
the user in the right direction,
https://community.cloudera.com/t5/Interactive-Short-cycle-SQL/Query-blah-expired-due-to-client-inactivity-timeout-is-10m/m-p/66842.
Maybe the error reporting isn't worth the other hassles though - or maybe we
just need to set clearer expectations for client behaviour - that they need to
handle sessions being terminated in this way.
> Implement support for closing idle sessions
> -------------------------------------------
>
> Key: IMPALA-7802
> URL: https://issues.apache.org/jira/browse/IMPALA-7802
> Project: IMPALA
> Issue Type: Improvement
> Components: Clients
> Affects Versions: Impala 3.0, Impala 2.12.0
> Reporter: Michael Ho
> Assignee: Zoram Thanga
> Priority: Critical
> Labels: supportability
>
> Currently, the query option {{idle_session_timeout}} specifies a timeout in
> seconds after which all running queries of that idle session will be
> cancelled and no new queries can be issued to it. However, the idle session
> will remain open and it needs to be closed explicitly. Please see the
> [documentation|https://www.cloudera.com/documentation/enterprise/latest/topics/impala_idle_session_timeout.html]
> for details.
> This behavior may be undesirable as each session still consumes an Impala
> frontend service thread. The number of frontend service threads is bound by
> the flag {{fe_service_threads}}. So, in a multi-tenant environment, an Impala
> server can have a lot of idle sessions but they still consume against the
> quota of {{fe_service_threads}}. If the number of sessions established
> reaches {{fe_service_threads}}, all new session creations will block until
> some of the existing sessions exit. There may be no time bound on when these
> zombie idle sessions will be closed and it's at the mercy of the client
> implementation to close them. In some sense, leaving many idle sessions open
> is a way to launch a denial of service attack on Impala.
> To fix this situation, we should have an option to forcefully close a session
> when it's considered idle so it won't unnecessarily consume the limited
> number of frontend service threads. cc'ing [~zoram]
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