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Posted to issues-all@impala.apache.org by "Manish Maheshwari (JIRA)" <ji...@apache.org> on 2019/04/08 02:29:00 UTC
[jira] [Commented] (IMPALA-7802) Implement support for closing idle
sessions
[ https://issues.apache.org/jira/browse/IMPALA-7802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16812035#comment-16812035 ]
Manish Maheshwari commented on IMPALA-7802:
-------------------------------------------
A badly designed impala client did not close the connections and I had 18,000 connections pile up on 4 coordinators causing an impala service outage. There seems to be no benefit of keeping this session open as the doc clearly says `The session remains open, but the only operation you can perform is to close it.`.
> 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
> 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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