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https://issues.apache.org/jira/browse/HDFS-9700?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15348970#comment-15348970
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Colin Patrick McCabe commented on HDFS-9700:
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Hmm. I think it's confusing to use a configuration key for Hadoop RPC to
configure something that isn't Hadoop RPC. We have tons of keys named with
{{ipc}} and all of them relate to Hadoop RPC, not to DataTransferProtocol.
{{ipc.client.connect.max.retries}}, {{ipc.server.listen.queue.size}},
{{ipc.client.connect.timeout}}, and so forth.
There are valid cases where you might want a different configuration for RPC
versus datatransferprotocol. For example, conservative users might also want
to avoid turning on {{TCP_NODELAY}} for {{DataTransferProtocol}} since it is a
new feature, and not as well tested as doing what we do currently. But since
we have {{TCP_NODELAY}} on for RPC, they might want to keep that on.
I agree that in the long term, {{TCP_NODELAY}} should be used for both. But
that's an argument for removing the configuration altogether, not for making it
do something other than what it's named.
> DFSClient and DFSOutputStream should set TCP_NODELAY on sockets for
> DataTransferProtocol
> ----------------------------------------------------------------------------------------
>
> Key: HDFS-9700
> URL: https://issues.apache.org/jira/browse/HDFS-9700
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 2.7.1, 2.6.3
> Reporter: Gary Helmling
> Assignee: Gary Helmling
> Fix For: 2.8.0
>
> Attachments: HDFS-9700-branch-2.7.002.patch,
> HDFS-9700-branch-2.7.003.patch, HDFS-9700-v1.patch, HDFS-9700-v2.patch,
> HDFS-9700.002.patch, HDFS-9700.003.patch, HDFS-9700.004.patch,
> HDFS-9700_branch-2.7-v2.patch, HDFS-9700_branch-2.7.patch
>
>
> In {{DFSClient.connectToDN()}} and
> {{DFSOutputStream.createSocketForPipeline()}}, we never call
> {{setTcpNoDelay()}} on the constructed socket before sending. In both cases,
> we should respect the value of ipc.client.tcpnodelay in the configuration.
> While this applies whether security is enabled or not, it seems to have a
> bigger impact on latency when security is enabled.
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