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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13065) Add a new interface for retrieving FS and FC Statistics
Date Tue, 03 May 2016 08:58:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15268386#comment-15268386
] 

Steve Loughran commented on HADOOP-13065:
-----------------------------------------

Related to this, I've come across some details about how the reflection-based {{AtomicLongFieldUpdater}}
is going to become a lot closer to non-atomic {{volatile long ++}} calls: http://shipilev.net/blog/2015/faster-atomic-fu/

This argues in favour of using this operation for updating metrics directly...it'd mean that
the variables could just be simple {{volatile long}}, with a static {{AtomicLongFieldUpdater}}
used to update them all

{code}
public final class readMetrics {

private static final AtomicLongFieldUpdater bytesReadUpdater = AtomicLongFieldUpdater.newUpdater(Cell.class,
"bytesRead");
private volatile long bytesRead;

public long incBytesRead(long count) {
  return bytesReadUpdater.addAndGet(count);
}
{code}

HBase uses this in {{org.apache.hadoop.hbase.util.Counter}}, where it's described as "High
scalable counter. Thread safe."


> Add a new interface for retrieving FS and FC Statistics
> -------------------------------------------------------
>
>                 Key: HADOOP-13065
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13065
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>            Reporter: Ram Venkatesh
>            Assignee: Mingliang Liu
>         Attachments: HADOOP-13065-007.patch, HDFS-10175.000.patch, HDFS-10175.001.patch,
HDFS-10175.002.patch, HDFS-10175.003.patch, HDFS-10175.004.patch, HDFS-10175.005.patch, HDFS-10175.006.patch,
TestStatisticsOverhead.java
>
>
> Currently FileSystem.Statistics exposes the following statistics:
> BytesRead
> BytesWritten
> ReadOps
> LargeReadOps
> WriteOps
> These are in-turn exposed as job counters by MapReduce and other frameworks. There is
logic within DfsClient to map operations to these counters that can be confusing, for instance,
mkdirs counts as a writeOp.
> Proposed enhancement:
> Add a statistic for each DfsClient operation including create, append, createSymlink,
delete, exists, mkdirs, rename and expose them as new properties on the Statistics object.
The operation-specific counters can be used for analyzing the load imposed by a particular
job on HDFS. 
> For example, we can use them to identify jobs that end up creating a large number of
files.
> Once this information is available in the Statistics object, the app frameworks like
MapReduce can expose them as additional counters to be aggregated and recorded as part of
job summary.



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