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https://issues.apache.org/jira/browse/HDFS-4049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13476171#comment-13476171
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Colin Patrick McCabe commented on HDFS-4049:
--------------------------------------------
Looks good. It makes sense to use only one buffer for this.
It looks like Java doesn't expose {{writev}} in this case, which is what we
would need to write multiple buffers as one packet with {{TCP_NODELAY}}.
(Although there is a multi-buffer write method in {{FileChannel}}, I didn't
find one for {{DataOutputStream}}).
{code}
@@ -100,12 +102,17 @@ public void run() {
}
} catch (Throwable t) {
thrown.compareAndSet(null, t);
+ } finally {
+
}
}
{code}
Extra code?
Does it make sense to add a test for the numDataNodes = 1, repl = 1 case?
> hflush performance regression due to nagling delays
> ---------------------------------------------------
>
> Key: HDFS-4049
> URL: https://issues.apache.org/jira/browse/HDFS-4049
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: data-node, performance
> Affects Versions: 3.0.0, 2.0.2-alpha
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Critical
> Attachments: hdfs-4049.txt
>
>
> HDFS-3721 reworked the way that packets are mirrored through the pipeline in
> the datanode. This caused two write() calls where there used to be one, which
> interacts badly with nagling so that there are 40ms bubbles on hflush()
> calls. We didn't notice this in the tests because the hflush perf test only
> uses a single datanode.
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