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From "Vihang Karajgaonkar (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-15879) Fix HiveMetaStoreChecker.checkPartitionDirs method
Date Tue, 28 Feb 2017 21:39:45 GMT

    [ https://issues.apache.org/jira/browse/HIVE-15879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15888910#comment-15888910
] 

Vihang Karajgaonkar commented on HIVE-15879:
--------------------------------------------

Created HIVE-16059

> Fix HiveMetaStoreChecker.checkPartitionDirs method
> --------------------------------------------------
>
>                 Key: HIVE-15879
>                 URL: https://issues.apache.org/jira/browse/HIVE-15879
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Vihang Karajgaonkar
>            Assignee: Vihang Karajgaonkar
>             Fix For: 2.2.0
>
>         Attachments: HIVE-15879.01.patch, HIVE-15879.02.patch, HIVE-15879.03.patch, HIVE-15879.04.patch
>
>
> HIVE-15803 fixes the msck hang issue in HiveMetaStoreChecker.checkPartitionDirs method
by adding a check to see if the Threadpool has any spare threads. If not it uses single threaded
listing of the files.
> {noformat}
>     if (pool != null) {
>       synchronized (pool) {
>         // In case of recursive calls, it is possible to deadlock with TP. Check TP usage
here.
>         if (pool.getActiveCount() < pool.getMaximumPoolSize()) {
>           useThreadPool = true;
>         }
>         if (!useThreadPool) {
>           if (LOG.isDebugEnabled()) {
>             LOG.debug("Not using threadPool as active count:" + pool.getActiveCount()
>                 + ", max:" + pool.getMaximumPoolSize());
>           }
>         }
>       }
>     }
> {noformat}
> Based on the java doc of getActiveCount() below 
> bq. Returns the approximate number of threads that are actively executing tasks.
> it returns only approximate number of threads and it cannot be guaranteed that it always
returns the exact number of active threads. This still exposes the method implementation to
the msck hang bug in rare corner cases.
> We could either:
> 1. Use a atomic counter to track exactly how many threads are actively running
> 2. Relook at the method itself to make it much simpler. Like eg, look into the possibility
of changing the recursive implementation to an iterative implementation where worker threads
pick tasks from a queue until the queue is empty.



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