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https://issues.apache.org/jira/browse/HDFS-5644?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13843396#comment-13843396
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Colin Patrick McCabe commented on HDFS-5644:
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libhdfs doesn't actually use locking to get the JNI environment. It uses
thread-local data for that, since you need a different {{JNIEnv}} per thread.
The shared hash table stores global class references. Since this is
insert-only (we never remove elements), and we should not need to resize this
if we choose the initial size properly, it would be relatively easy to create a
concurrent version of this.
> Reduce lock contention in libhdfs.
> ----------------------------------
>
> Key: HDFS-5644
> URL: https://issues.apache.org/jira/browse/HDFS-5644
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: libhdfs
> Affects Versions: 3.0.0, 2.2.0
> Reporter: Chris Nauroth
>
> libhdfs uses locking internally for coordinating access to shared hash tables
> and the JNI environment. The scope of this issue is to improve performance
> of libhdfs by reducing lock contention.
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