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https://issues.apache.org/jira/browse/HDFS-11280?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15788274#comment-15788274
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Zheng Shao commented on HDFS-11280:
-----------------------------------
> The patch doesn't appear to include any new or modified tests. Please justify
> why no new tests are needed for this patch. Also please list what manual
> steps were performed to verify this patch.
In order to verify the HTTP Keep Alive is enabled, we need to look at network
stats at system level (using netstat for example) and that is
platform-dependent. It's not a good test to mock the underlying UrlConnection
using factory because the contract to the tested (getInputStrea().close()
trigger HTTP Keep-Alive is in JDK's HttpUrlConnection class, and mocking it out
defeats the purpose of testing).
Manual steps used to verify the bug fix is listed in the description.
> Allow WebHDFSClient to reuse HTTP connections (HTTP Keep-Alive)
> ---------------------------------------------------------------
>
> Key: HDFS-11280
> URL: https://issues.apache.org/jira/browse/HDFS-11280
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 2.7.3, 2.6.5, 3.0.0-alpha1
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Attachments: HDFS-11280.for.2.7.and.below.patch,
> HDFS-11280.for.2.8.and.beyond.2.patch, HDFS-11280.for.2.8.and.beyond.patch
>
>
> WebHDFSClient calls "conn.disconnect()", which disconnects from the NameNode.
> When we use webhdfs as the source in distcp, this used up all ephemeral
> ports on the client side since all closed connections continue to occupy the
> port with TIME_WAIT status for some time.
> According to http://tinyurl.com/java7-http-keepalive, we should call
> conn.getInputStream().close() instead to make sure the connection is kept
> alive. This will get rid of the ephemeral port problem.
> Manual steps used to verify the bug fix:
> 1. Build original hadoop jar.
> 2. Try out distcp from webhdfs as source, and "netstat -n | grep TIME_WAIT |
> grep -c 50070" on the local machine shows a big number (100s).
> 3. Build hadoop jar with this diff.
> 4. Try out distcp from webhdfs as source, and "netstat -n | grep TIME_WAIT |
> grep -c 50070" on the local machine shows 0.
> 5. The explanation: distcp's client side does a lot of directory scanning,
> which would create and close a lot of connections to the namenode HTTP port.
> Reference:
> 2.7 and below:
> https://github.com/apache/hadoop/blob/branch-2.6/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/web/WebHdfsFileSystem.java#L743
> 2.8 and above:
> https://github.com/apache/hadoop/blob/branch-2.8/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/WebHdfsFileSystem.java#L898
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