[jira] [Created] (HDFS-12332) Logging improvement suggestion for SampleStat function MinMax.add

["Xu Zhao (JIRA)" <ji...@apache.org>]

Xu Zhao created HDFS-12332:
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             Summary: Logging improvement suggestion for SampleStat function MinMax.add
                 Key: HDFS-12332
                 URL: https://issues.apache.org/jira/browse/HDFS-12332
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: metrics
    Affects Versions: 3.0.0-alpha4
            Reporter: Xu Zhao
            Priority: Minor


In order to debug performance anomlies, it is better to see when the max and min value get updated in metrics.
For example, in our workload we would like to see the longest latency of a write block request on DataNode.

The following metric updating code could possibly update the min/max value in SampleStat class:

{code:java}
    datanode.getMetrics().addWriteBlockOp(elapsed());
    datanode.getMetrics().incrWritesFromClient(peer.isLocal(), size);
{code}

Here I am attaching an attempt to patch it.
The patch just adds additional DEBUG level logging in the MinMax class and prints the new value when it gets updated.

Please let me know what you think. For example, if this patch would introduce too much noises, what is the best way to trace the read/writeBlock that has the minimum/maximum latency?
Any comments are appreciated!



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