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