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https://issues.apache.org/jira/browse/HADOOP-13065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15273605#comment-15273605
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Colin Patrick McCabe commented on HADOOP-13065:
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Thanks for the reviews.
bq. in FileSystem.getStatistics(), For performance, you could try using
ConcurrentMap for the map, and only if it is not present create the objects and
call putIfAbsent() (or a synchronized block create and update the maps (with a
second lookup there to eliminate the small race condition). This will eliminate
the sync point on a simple lookup when the entry exists.
Hmm. I don't think that we really need to optimize this function. When using
the new API, the only time this function gets called is when a new FileSystem
object is created, which should be very rare.
bq. For testing a may to reset/remove an entry could be handy.
We do have some tests that zero out the existing statistics objects. I'm not
sure if removing the entry really gets us more coverage than we have now, since
we know that it was created by this code path (therefore the code path was
tested).
bq. That's said, we can firstly deprecate the FileSystem#getStatistics()?
Agree.
> 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, HADOOP-13065.008.patch,
> HADOOP-13065.009.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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