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From Yongzhi Chen <yc...@cloudera.com>
Subject Re: Review Request 52559: HIVE-14799: Query operation are not thread safe during its cancellation
Date Thu, 13 Oct 2016 18:39:52 GMT

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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/52559/#review152556
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It is not thread safe for releaseDriverContext can be called in compling mode from cancel,
but seems only null value matters. So use the local variable(driverCxt) to avoid NPE after
the close() is called from cancel?

- Yongzhi Chen


On Oct. 12, 2016, 4:31 a.m., Chaoyu Tang wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/52559/
> -----------------------------------------------------------
> 
> (Updated Oct. 12, 2016, 4:31 a.m.)
> 
> 
> Review request for hive, Sergey Shelukhin, Thejas Nair, Vaibhav Gumashta, and Yongzhi
Chen.
> 
> 
> Bugs: HIVE-14799
>     https://issues.apache.org/jira/browse/HIVE-14799
> 
> 
> Repository: hive-git
> 
> 
> Description
> -------
> 
> This patch is going to fix a couple of Driver issues related to the close request from
a thread other than the one running the query (e.g. from SQLOperation cancel via Timeout or
Ctrl-C):
> 1. Driver is not thread safe and usually supports only one thread at time since it has
variables like ctx, plan which are not thread protected. But certain special use cases need
access the Driver objects from multiply threads. For example, when a query runs in a background
thread, driver.close is invoked in another thread by the query timeout (see HIVE-4924). The
close process could nullify the shared variables like ctx which could cause NPE in the other
query thread which is using them. This runtime exception is unpredictable and not well handled
in the code. Some resources (e.g. locks, files) are left behind and not be cleaned because
there are no more available = references to them. In this patch, I use the waiting in the
close which makes sure only one thread uses these variables and the resource cleaning happens
after the query finished (or interrupted).
> 2. SQLOperation.cancel sends the interrupt signal to the background thread running the
query (via backgroundHandle.cancel(true)) but it could not stop that process since there is
no code to capture the signal in the process. In another word, current timeout code could
not gracefully and promptly stop the query process, though it could eventually stop the process
by killing the running tasks (e.g. MapRedTask) via driverContext.shutdown (see HIVE-5901).
So in the patch, I added a couple of checkpoints to intercept the interrupt signal either
set by close method (a volatile variable) or thread.interrupt. They should be helpful to capture
these signals earlier , though not intermediately.
> 
> 
> Diffs
> -----
> 
>   ql/src/java/org/apache/hadoop/hive/ql/Driver.java dd55434 
> 
> Diff: https://reviews.apache.org/r/52559/diff/
> 
> 
> Testing
> -------
> 
> Manually tests
> Precommit tests
> 
> 
> Thanks,
> 
> Chaoyu Tang
> 
>


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