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Posted to common-dev@hadoop.apache.org by "Raghu Angadi (JIRA)" <ji...@apache.org> on 2008/07/02 00:52:45 UTC
[jira] Commented: (HADOOP-3672) support for persistent connections
to improve random read performance.
[ https://issues.apache.org/jira/browse/HADOOP-3672?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12609740#action_12609740 ]
Raghu Angadi commented on HADOOP-3672:
--------------------------------------
What is the avg size of pread()? Could you attach your benchmark to the jira?
> support for persistent connections to improve random read performance.
> ----------------------------------------------------------------------
>
> Key: HADOOP-3672
> URL: https://issues.apache.org/jira/browse/HADOOP-3672
> Project: Hadoop Core
> Issue Type: Improvement
> Components: dfs
> Affects Versions: 0.17.0
> Environment: Linux 2.6.9-55 , Dual Core Opteron 280 2.4Ghz , 4GB memory
> Reporter: George Wu
>
> 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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