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https://issues.apache.org/jira/browse/HIVE-20682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16665492#comment-16665492
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Sankar Hariappan edited comment on HIVE-20682 at 10/31/18 7:03 AM:
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[~pvary], Thanks for your thoughts!
* H1 is sessionHive object and will be preserved in session object through out
the life time of session. HMS connection of sessionHive will be closed only
when we close the session.
* H2 is local to given thread and will be closed when we set sessionHive again
in next query. ThreadLocalHive.set() method closes the previous thread local
Hive object H2 before overwriting it.
* Also, if an async thread reallocates Hive object (let's say H3), then it
will be closed by Hive.closeCurrent call when the thread exits.
* So, I don't think there would be any HMS connection leak here.
* parentHive is always sessionHive object where allowClose flag is false. So,
the "assert (!parentHive.allowClose());" will never fail.
But I agree, there is a chance that each and every query re-creates Hive object
if the HMS relevant configs are changed in between queries. I missed this part
where sessionConf would be changed when user sets any Hive configurations via
cli.
So, I think, the earlier thread reference count solution would solve this
issue. [~maheshk114], please comment if you think otherwise.
cc [~daijy], [~thejas]
was (Author: sankarh):
[~pvary], Thanks for your thoughts!
* H1 is sessionHive object and will be preserved in session object through out
the life time of session. HMS connection of sessionHive will be closed only
when we close the session.
* H2 is local to given thread and will be closed when we set sessionHive again
in next query. ThreadLocalHive.set() method closes the previous thread local
Hive object H2 before overwriting it.
* Also, if an async thread reallocates Hive object (let's say H3), then it
will be closed by Hive.closeCurrent call when the thread exits.
* So, I don't think there would be any HMS connection leak here.
* parentHive is always sessionHive object where allowClose flag is false. So,
the "assert (!parentHive.allowClose());" will never fail.
But I agree, there is a chance that each and every query re-creates Hive object
if the HMS relevant configs are changed in between queries. I missed this part
where sessionConf would be changed when user sets any Hive configurations via
cli.
So, I think, the earlier thread reference count solution would solve this
issue. [~maheshk114], please comment if you think otherwise.
cc [~daijy], [~thejas], [~maheshk114]
> 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
>
>
> *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.
> cc [~pvary]
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