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https://issues.apache.org/jira/browse/HDFS-8696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14935932#comment-14935932
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Xiaobing Zhou commented on HDFS-8696:
-------------------------------------
Checked the test failures are not related.
> Reduce the variances of latency of WebHDFS
> ------------------------------------------
>
> Key: HDFS-8696
> URL: https://issues.apache.org/jira/browse/HDFS-8696
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: webhdfs
> Affects Versions: 2.7.0
> Reporter: Xiaobing Zhou
> Assignee: Xiaobing Zhou
> Attachments: HDFS-8696.004.patch, HDFS-8696.005.patch,
> HDFS-8696.006.patch, HDFS-8696.007.patch, HDFS-8696.008.patch,
> HDFS-8696.009.patch, HDFS-8696.010.patch, HDFS-8696.1.patch,
> HDFS-8696.2.patch, HDFS-8696.3.patch
>
>
> There is an issue that appears related to the webhdfs server. When making two
> concurrent requests, the DN will sometimes pause for extended periods (I've
> seen 1-300 seconds), killing performance and dropping connections.
> To reproduce:
> 1. set up a HDFS cluster
> 2. Upload a large file (I was using 10GB). Perform 1-byte reads, writing
> the time out to /tmp/times.txt
> {noformat}
> i=1
> while (true); do
> echo $i
> let i++
> /usr/bin/time -f %e -o /tmp/times.txt -a curl -s -L -o /dev/null
> "http://<namenode>:50070/webhdfs/v1/tmp/bigfile?op=OPEN&user.name=root&length=1";
> done
> {noformat}
> 3. Watch for 1-byte requests that take more than one second:
> tail -F /tmp/times.txt | grep -E "^[^0]"
> 4. After it has had a chance to warm up, start doing large transfers from
> another shell:
> {noformat}
> i=1
> while (true); do
> echo $i
> let i++
> /usr/bin/time -f %e curl -s -L -o /dev/null
> "http://<namenode>:50070/webhdfs/v1/tmp/bigfile?op=OPEN&user.name=root";
> done
> {noformat}
> It's easy to find after a minute or two that small reads will sometimes
> pause for 1-300 seconds. In some extreme cases, it appears that the
> transfers timeout and the DN drops the connection.
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