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From "Thejas M Nair (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-17502) Reuse of default session should not throw an exception in LLAP w/ Tez
Date Mon, 09 Oct 2017 23:32:00 GMT

    [ https://issues.apache.org/jira/browse/HIVE-17502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16197870#comment-16197870
] 

Thejas M Nair commented on HIVE-17502:
--------------------------------------

[~thai.bui]
Do you know why Hue uses same HiveServer2 session for multiple queries ?
I fear this is mostly kicking can down the road as we don't seem to have all cases covered
here or any ongoing investment to cover those cases, that I am aware of.
In general, with JDBC,  recommendations people have seem to be to not run simultaneous queries
within same jdbc connection. (Also, jdbc statement calls are blocking, so its not easy to
do without multiple threads).
Is it possible to change Hue to use different sessions for each query ?
We can still get this patch in, but I just want to get the conversation going on the long
term solution for this.


> Reuse of default session should not throw an exception in LLAP w/ Tez
> ---------------------------------------------------------------------
>
>                 Key: HIVE-17502
>                 URL: https://issues.apache.org/jira/browse/HIVE-17502
>             Project: Hive
>          Issue Type: Bug
>          Components: llap, Tez
>    Affects Versions: 2.1.1, 2.2.0
>         Environment: HDP 2.6.1.0-129, Hue 4
>            Reporter: Thai Bui
>            Assignee: Thai Bui
>             Fix For: 3.0.0
>
>         Attachments: HIVE-17502.patch
>
>
> Hive2 w/ LLAP on Tez doesn't allow a currently used, default session to be skipped mostly
because of this line https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezSessionPoolManager.java#L365.
> However, some clients such as Hue 4, allow multiple sessions to be used per user. Under
this configuration, a Thrift client will send a request to either reuse or open a new session.
The reuse request could include the session id of a currently used snippet being executed
in Hue, this causes HS2 to throw an exception:
> {noformat}
> 2017-09-10T17:51:36,548 INFO  [Thread-89]: tez.TezSessionPoolManager (TezSessionPoolManager.java:canWorkWithSameSession(512))
- The current user: hive, session user: hive
> 2017-09-10T17:51:36,549 ERROR [Thread-89]: exec.Task (TezTask.java:execute(232)) - Failed
to execute tez graph.
> org.apache.hadoop.hive.ql.metadata.HiveException: The pool session sessionId=5b61a578-6336-41c5-860d-9838166f97fe,
queueName=llap, user=hive, doAs=false, isOpen=true, isDefault=true, expires in 591015330ms
should have been returned to the pool
> 	at org.apache.hadoop.hive.ql.exec.tez.TezSessionPoolManager.canWorkWithSameSession(TezSessionPoolManager.java:534)
~[hive-exec-2.1.0.2.6.1.0-129.jar:2.1.0.2.6.1.0-129]
> 	at org.apache.hadoop.hive.ql.exec.tez.TezSessionPoolManager.getSession(TezSessionPoolManager.java:544)
~[hive-exec-2.1.0.2.6.1.0-129.jar:2.1.0.2.6.1.0-129]
> 	at org.apache.hadoop.hive.ql.exec.tez.TezTask.execute(TezTask.java:147) [hive-exec-2.1.0.2.6.1.0-129.jar:2.1.0.2.6.1.0-129]
> 	at org.apache.hadoop.hive.ql.exec.Task.executeTask(Task.java:197) [hive-exec-2.1.0.2.6.1.0-129.jar:2.1.0.2.6.1.0-129]
> 	at org.apache.hadoop.hive.ql.exec.TaskRunner.runSequential(TaskRunner.java:100) [hive-exec-2.1.0.2.6.1.0-129.jar:2.1.0.2.6.1.0-129]
> 	at org.apache.hadoop.hive.ql.exec.TaskRunner.run(TaskRunner.java:79) [hive-exec-2.1.0.2.6.1.0-129.jar:2.1.0.2.6.1.0-129]
> {noformat}
> Note that every query is issued as a single 'hive' user to share the LLAP daemon pool,
a set of pre-determined number of AMs is initialized at setup time. Thus, HS2 should allow
new sessions from a Thrift client to be used out of the pool, or an existing session to be
skipped and an unused session from the pool to be returned. The logic to throw an exception
in the  `canWorkWithSameSession` doesn't make sense to me.
> I have a solution to fix this issue in my local branch at https://github.com/thaibui/hive/commit/078a521b9d0906fe6c0323b63e567f6eee2f3a70.
When applied, the log will become like so
> {noformat}
> 2017-09-10T09:15:33,578 INFO  [Thread-239]: tez.TezSessionPoolManager (TezSessionPoolManager.java:canWorkWithSameSession(533))
- Skipping default session sessionId=6638b1da-0f8a-405e-85f0-9586f484e6de, queueName=llap,
user=hive, doAs=false, isOpen=true, isDefault=true, expires in 591868732ms since it is being
used.
> {noformat}
> A test case is provided in my branch to demonstrate how it works. If possible I would
like this patch to be applied to version 2.1, 2.2 and master. Since we are using 2.1 LLAP
in production with Hue 4, this patch is critical to our success.
> Alternatively, if this patch is too broad in scope, I propose adding an option to allow
"skipping of currently used default sessions". With this new option default to "false", existing
behavior won't change unless the option is turned on.
> I will prepare an official path if this change to master &/ the other branches is
acceptable. I'm not an contributor &/ committer, this will be my first time contributing
to Hive and the Apache foundation. Any early review is greatly appreciated, thanks!



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