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https://issues.apache.org/jira/browse/HDFS-380?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Todd Lipcon resolved HDFS-380.
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Resolution: Duplicate
Resolving as duplicate of HDFS-941
> support for persistent connections to improve random read performance.
> ----------------------------------------------------------------------
>
> Key: HDFS-380
> URL: https://issues.apache.org/jira/browse/HDFS-380
> Project: Hadoop HDFS
> Issue Type: Improvement
> Environment: Linux 2.6.9-55 , Dual Core Opteron 280 2.4Ghz , 4GB
> memory
> Reporter: George Wu
> Attachments: pread_test.java
>
>
> preads() establish new connections per request. yourkit java profiles show
> that this connection overhead is pretty significant on the DataNode.
> I wrote a simple microbenchmark program which does many iterations of pread()
> from different offsets of a large file. I hacked DFSClient/DataNode code to
> re-use the same connection/DataNode request handler thread. The performance
> improvement was 7% when the data is served from disk and 80% when the data is
> served from the OS page cache.
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