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https://issues.apache.org/jira/browse/HDFS-1323?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12894072#action_12894072
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Jay Booth commented on HDFS-1323:
---------------------------------
Correction - the patch created a 10% performance increase for HBase random
GETs. It was probably a larger % of the read operation, if you don't include
other work by HBase.
> Pool/share file channels for HDFS read
> --------------------------------------
>
> Key: HDFS-1323
> URL: https://issues.apache.org/jira/browse/HDFS-1323
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node
> Reporter: Jay Booth
> Fix For: 0.20-append, 0.22.0
>
> Attachments: hdfs-1323-20100730.patch
>
>
> Currently, all reads in HDFS require opening and closing the underlying
> block/meta filechannels. We could pool these filechannels and save some
> system calls and other work. Since HDFS read requests can be satisfied by
> positioned reads and transferTos, we can even share these filechannels
> between concurrently executing requests.
> The attached patch was benchmarked as part of work on HDFS-918 and exhibited
> a 10% performance increase for small random reads.
> This does not affect client logic and involves minimal change to server
> logic. Patch is based on branch 20-append.
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