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https://issues.apache.org/jira/browse/HIVE-17502?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16165060#comment-16165060
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Thai Bui commented on HIVE-17502:
---------------------------------
[~sershe] Thanks for the prompt reply. I see that the SessionState.get keeps a
thread's static SessionState object which gets set/unset every time a session
is returned to the pool. I'm not that familiar with Hive/TezPool/TezTask
session code base, but given that it is thread local, it shouldn't impact other
thread's and/or client, correct?
Also, to help us understand my use case a little bit better, I will try to
elaborate what I'm trying to do a little bit better.
Let's say a client C1 requests for a new session, it is handled by thread T1 in
HS2, which yields session S1 from the pool. The same client C1 wants to make a
parallel request and reuses S1's in the request. Now, since S1 is still being
used, the session pool should skip S1 and returns S2 from the pool, given that
S2 is unused.
Since, S2 should be created by another thread T2 since T1 was busy executing
the TezTask in the first request in HS2. Given that SessionState.get is
thread's local to only T1, T2 should gets a different SessionState.get, which
yield a different SessionState. But I think that is not the case,
SessionState.get will always yield the same currently used SessionState of the
client C1, which will be unset and that is problem, correct?
If that's the case, what's the best course of actions that I can take to make
parallel query execution of the same client in a session pool happen?
> 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
>
> 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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