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From "Sankar Hariappan (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HIVE-20682) Async query execution can potentially fail if shared sessionHive is closed by master thread.
Date Wed, 07 Nov 2018 17:19:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-20682?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sankar Hariappan updated HIVE-20682:
------------------------------------
    Status: Patch Available  (was: Open)

06.patch fixed test failure and windbags issue.

> Async query execution can potentially fail if shared sessionHive is closed by master
thread.
> --------------------------------------------------------------------------------------------
>
>                 Key: HIVE-20682
>                 URL: https://issues.apache.org/jira/browse/HIVE-20682
>             Project: Hive
>          Issue Type: Bug
>          Components: HiveServer2
>    Affects Versions: 3.1.0, 4.0.0
>            Reporter: Sankar Hariappan
>            Assignee: Sankar Hariappan
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: HIVE-20682.01.patch, HIVE-20682.02.patch, HIVE-20682.03.patch, HIVE-20682.04.patch,
HIVE-20682.05.patch, HIVE-20682.06.patch
>
>
> *Problem description:*
> The master thread initializes the *sessionHive* object in *HiveSessionImpl* class when we
open a new session for a client connection and by default all queries from this connection shares
the same sessionHive object. 
> If the master thread executes a *synchronous* query, it closes the sessionHive object
(referred via thread local hiveDb) if  {{Hive.isCompatible}} returns false and sets new Hive
object in thread local HiveDb but doesn't change the sessionHive object in the session. Whereas,
*asynchronous* query execution via async threads never closes the sessionHive object and
it just creates a new one if needed and sets it as their thread local hiveDb.
> So, the problem can happen in the case where an *asynchronous* query is being executed
by async threads refers to sessionHive object and the master thread receives a *synchronous*
query that closes the same sessionHive object. 
> Also, each query execution overwrites the thread local hiveDb object to sessionHive object
which potentially leaks a metastore connection if the previous synchronous query execution
re-created the Hive object.
> *Possible Fix:*
> The *sessionHive* object could be shared my multiple threads and so it shouldn't be allowed
to be closed by any query execution threads when they re-create the Hive object due to changes
in Hive configurations. But the Hive objects created by query execution threads should be
closed when the thread exits.
> So, it is proposed to have an *isAllowClose* flag (default: *true*) in Hive object which
should be set to *false* for *sessionHive* and would be forcefully closed when the session
is closed or released.
> Also, when we reset *sessionHive* object with new one due to changes in *sessionConf*,
the old one should be closed when no async thread is referring to it. This can be done using
"*finalize*" method of Hive object where we can close HMS connection when Hive object is garbage
collected.
> cc [~pvary]



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