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From "marco polo (JIRA)" <j...@apache.org>
Subject [jira] [Created] (ACCUMULO-3835) TabletServerBatchReaderIterator
Date Wed, 20 May 2015 15:51:59 GMT
marco polo created ACCUMULO-3835:
------------------------------------

             Summary: TabletServerBatchReaderIterator
                 Key: ACCUMULO-3835
                 URL: https://issues.apache.org/jira/browse/ACCUMULO-3835
             Project: Accumulo
          Issue Type: Bug
          Components: client
    Affects Versions: 1.6.2
            Reporter: marco polo


When running many batch scanners in a JVM, we see a significant amount of cache invalidation
within the JVM when we prematurely close the batch scanner. When we prematurely close the
batch scanner ( and threads within it are running an interrupt is sent to those threads, causing
them to add the extents to the failures map and invalidate the cache. This causes lock contention
on the write lock for the TabletLocatorImpl.

The lock contention hinders performance in a highly parallel client that does not need to
invalid the cache as a result of being stopped. 

As a positive test to ensure this was my problem I added a conditional check to the IOException
handler in the run method of TabletServerBatchReaderIterator. The conditional checked whether
the query thread pool was shut down. If it was not, we would invalidate the cache as we can
assume the reason likely wasn't interruption. If it was shut down, we would not invalide the
cache. This reduced lock contention dramatically and reduced runtime. This should cause no
harm as any other failure would cause cache invalidation through some other route. 



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