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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-380) support for persistent connections to improve random read performance.
Date Wed, 23 Mar 2011 21:03:06 GMT

    [ https://issues.apache.org/jira/browse/HDFS-380?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13010445#comment-13010445
] 

Kihwal Lee commented on HDFS-380:
---------------------------------

I think this issue can be duped to 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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