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From sachouche <...@git.apache.org>
Subject [GitHub] drill pull request #1087: Attempt to fix memory leak in Parquet
Date Tue, 09 Jan 2018 23:54:10 GMT
GitHub user sachouche opened a pull request:

    https://github.com/apache/drill/pull/1087

    Attempt to fix memory leak in Parquet

    ** Problem Description **
    This is an extremely rare leak which I was able to emulate by putting a sleep in the AsyncPageReader
right after reading the page and before enqueue in the result queue. This is how this issue
could manifest itself in real life scenario:
    - AsyncPageReader reads a page into a buffer but didn't enqueue yet the result (thread
got preempted)
    - Parquet Scan thread blocked waiting on the task (Future object dequeued)
    - Cancel received and Scan thread interrupted 
    - Future.get() returns (Future object is lost)
    - Scan thread executes release logic
    - Scan thread is not able to interrupt the AsyncPageReader thread since the future object
is lost
    -  AsyncPageReader thread resumes and enqueues the DrillBuf in the result queue
    - This results in a leak since this buffer is not properly released
    
    ** Fix Description **
    - The fix is straightforward as we peek the Future object during the blocking get() method
    - This way, an exception (such as an interrupt) will leave the Future object in the task
queue
    - The cleanup logic will be able to guarantee the DrillBuf object is either GCed by the
AsyncPageReader or ParquetScan thread

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

    $ git pull https://github.com/sachouche/drill DRILL-6079

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

    https://github.com/apache/drill/pull/1087.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 #1087
    
----
commit 52030d1d9cc3b8992a10ade8c7126d66e785043a
Author: Salim Achouche <sachouche2@...>
Date:   2017-12-22T19:50:56Z

    Attempt to fix memory leak in Parquet

----


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