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https://issues.apache.org/jira/browse/HDFS-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13050622#comment-13050622
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Kihwal Lee commented on HDFS-941:
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>Also with 128 MB file everything is in RAM, not sure what it measures.
If cold reads are performed, the disk i/o will be the bottleneck and that can
bury whatever overhead the patch might have introduced in the connection
handling under noise. Since the patch didn't change the rest of the serving
code, the ideal way of measuring its overhead will be having the dn to do
something like null ops. It is effectively putting a magnifying glass on the
area where the change has been made. In a normal setup, the next best thing is
probably what Todd did.
In any case, I will run DFSIO as you suggested.
> Datanode xceiver protocol should allow reuse of a connection
> ------------------------------------------------------------
>
> Key: HDFS-941
> URL: https://issues.apache.org/jira/browse/HDFS-941
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node, hdfs client
> Affects Versions: 0.22.0
> Reporter: Todd Lipcon
> Assignee: bc Wong
> Fix For: 0.22.0
>
> Attachments: 941.22.txt, 941.22.txt, 941.22.v2.txt, 941.22.v3.txt,
> HDFS-941-1.patch, HDFS-941-2.patch, HDFS-941-3.patch, HDFS-941-3.patch,
> HDFS-941-4.patch, HDFS-941-5.patch, HDFS-941-6.22.patch, HDFS-941-6.patch,
> HDFS-941-6.patch, HDFS-941-6.patch, fix-close-delta.txt, hdfs-941.txt,
> hdfs-941.txt, hdfs-941.txt, hdfs-941.txt, hdfs941-1.png
>
>
> Right now each connection into the datanode xceiver only processes one
> operation.
> In the case that an operation leaves the stream in a well-defined state (eg a
> client reads to the end of a block successfully) the same connection could be
> reused for a second operation. This should improve random read performance
> significantly.
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