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https://issues.apache.org/jira/browse/HDFS-10270?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15237396#comment-15237396
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Kihwal Lee commented on HDFS-10270:
-----------------------------------
It is not for testing the client connection being up. It is simply checking one
of the metrics values reported in JMX. I don't know the reason why
NumOpenConnections was chosen. The test had worked *reliably* until the jmx
caching was fixed. The values used to be available right away, but now it takes
about 10 seconds. So when it's working it adds about 10 more seconds of delay.
But the original author also made a wrong assumption. The assumption was that
the reason for the number of connections being 2 is due to having two
datanodes. As you have correctly analyzed, this is not true in a
MiniDFSCluster. Since the two datanodes are sharing the same JVM, a single
connection was shared for the {{DatanodeProtocol}}. An additional connection
was made for the client. In a real distributed cluster, it would have been 3
connections.
I lean toward fixing the existing check than removing it. First it shouldn't
check against the number of datanods, but simply 2. Regarding increasing ipc
client idle timeout, it will make test run time longer, which is against what
we have been trying to do. An alternative is to add a test resource to reduce
the jmx update interval. We could add a
{{hadoop-hdfs-project/hadoop-hdfs/src/test/resources/hadoop-metrics2.properties}}
file with one line containing {{*.period=1}}. This will also reduce the run
time of a number of test cases that query jmx to verify the result.
What do you think?
> TestJMXGet:testNameNode() fails
> -------------------------------
>
> Key: HDFS-10270
> URL: https://issues.apache.org/jira/browse/HDFS-10270
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: test
> Affects Versions: 3.0.0, 2.8.0
> Reporter: Andras Bokor
> Assignee: Gergely Novák
> Priority: Minor
> Attachments: HDFS-10270.001.patch, TestJMXGet.log, TestJMXGetFails.log
>
>
> It fails with java.util.concurrent.TimeoutException. Actually the problem
> here is that we expect 2 as NumOpenConnections metric but it is only 1. So
> the test waits 60 sec then fails.
> Please find maven output so the stack trace attached ([^TestJMXGetFails.log]).
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