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From "Josh Elser (JIRA)" <>
Subject [jira] [Commented] (ACCUMULO-3835) TabletServerBatchReaderIterator concurrency contention on early close()
Date Wed, 20 May 2015 16:51:00 GMT


Josh Elser commented on ACCUMULO-3835:

Seems reasonable to me. We should be able to discern the case when close() was called and
fail out gracefully and quickly.

> TabletServerBatchReaderIterator concurrency contention on early close()
> -----------------------------------------------------------------------
>                 Key: ACCUMULO-3835
>                 URL:
>             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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