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https://issues.apache.org/jira/browse/HDFS-14084?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16758718#comment-16758718
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Erik Krogen commented on HDFS-14084:
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Hey folks, I was testing out this patch and noticed an issue that I consider
pretty serious. When this is used in a standard DFS client, the
{{DefaultMetricsSystem}} singleton has never been initialized, so there is no
proper prefix to use for configurations, and numerous bits of testing code is
triggered. For example:
{code:title=MetricsSystemImpl#register()}
final String finalName = // be friendly to non-metrics tests
DefaultMetricsSystem.sourceName(name2, !monitoring);
{code}
With your patch, this is triggered when {{monitoring}} is false, which is
really only intended for testing AFAICT. This is the first instance I'm aware
of that is leveraging metrics2 for client-side metrics. I think it means that
we need to add a {{DefaultMetricsSystem.init("client")}} in the instantiation
of {{Client}}. It will need a corresponding {{shutdown()}}, probably on
{{Client#close()}}. Unfortunately both of these methods are expected to be only
called once, so we probably need to add some new mechanisms for a "conditional
initialization" that only initializes the system if this is the first call.
> Need for more stats in DFSClient
> --------------------------------
>
> Key: HDFS-14084
> URL: https://issues.apache.org/jira/browse/HDFS-14084
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 3.0.0
> Reporter: Pranay Singh
> Assignee: Pranay Singh
> Priority: Minor
> Attachments: HDFS-14084.001.patch, HDFS-14084.002.patch,
> HDFS-14084.003.patch, HDFS-14084.004.patch, HDFS-14084.005.patch,
> HDFS-14084.006.patch, HDFS-14084.007.patch, HDFS-14084.008.patch,
> HDFS-14084.009.patch, HDFS-14084.010.patch, HDFS-14084.011.patch,
> HDFS-14084.012.patch, HDFS-14084.013.patch, HDFS-14084.014.patch,
> HDFS-14084.015.patch, HDFS-14084.016.patch, HDFS-14084.017.patch,
> HDFS-14084.018.patch
>
>
> The usage of HDFS has changed from being used as a map-reduce filesystem, now
> it's becoming more of like a general purpose filesystem. In most of the cases
> there are issues with the Namenode so we have metrics to know the workload or
> stress on Namenode.
> However, there is a need to have more statistics collected for different
> operations/RPCs in DFSClient to know which RPC operations are taking longer
> time or to know what is the frequency of the operation.These statistics can
> be exposed to the users of DFS Client and they can periodically log or do
> some sort of flow control if the response is slow. This will also help to
> isolate HDFS issue in a mixed environment where on a node say we have Spark,
> HBase and Impala running together. We can check the throughput of different
> operation across client and isolate the problem caused because of noisy
> neighbor or network congestion or shared JVM.
> We have dealt with several problems from the field for which there is no
> conclusive evidence as to what caused the problem. If we had metrics or stats
> in DFSClient we would be better equipped to solve such complex problems.
> List of jiras for reference:
> -------------------------
> HADOOP-15538 HADOOP-15530 ( client side deadlock)
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