[jira] [Commented] (HIVE-20682) Async query execution can potentially fail if shared sessionHive is closed by master thread.

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-20682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16660488#comment-16660488 ] 

ASF GitHub Bot commented on HIVE-20682:
---------------------------------------

GitHub user sankarh opened a pull request:

    https://github.com/apache/hive/pull/452

    HIVE-20682: Async query execution can potentially fail if shared sessionHive is closed by master thread.

    

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/sankarh/hive HIVE-20682

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/hive/pull/452.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #452
    
----
commit 9f5a3eff3598d7b76fd7a53f6aedefd57e1c641e
Author: Sankar Hariappan <ma...@...>
Date:   2018-10-06T08:12:25Z

    HIVE-20682: Async query execution can potentially fail if shared sessionHive is closed by master thread.

----


> 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
>
>
> *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:*
> We shall maintain an Atomic reference counter in the Hive object. We increment the counter when somebody sets it in thread local hiveDb and decrement it when somebody releases it. Only when the counter is down to 0, we should close the connection.
> Couple of cases to release the thread local hiveDb:
>  * When synchronous query execution in master thread re-creates Hive object due to config change. We also, need to update the sessionHive object in the current session as we releases it from thread local hiveDb of master thread.
>  * When async thread exits after completing execution or due to exception.
> If the session is getting closed, it is guaranteed that the reference counter is down to 0 as we forcefully close all the async operations and so we can close the connection there.
> cc [~pvary]



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