Pool/share file channels for HDFS read
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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
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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