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From "Mingliang Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13065) Add a new interface for retrieving FS and FC Statistics
Date Wed, 04 May 2016 00:33:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15269925#comment-15269925
] 

Mingliang Liu commented on HADOOP-13065:
----------------------------------------

Hi [~cmccabe], I was addressing the initial use case following the newly designed API. The
two questions baffle me about the v8 patch. 1) How to maintain shared op->count storage
statistic for all file system objects and threads.  I think our use case does not need the
per-FileSystem stats like S3A. My first idea was to register a single instance to the global
storage statistics. 2) How to implement the single counter for each operation. As we need
the atomic increment support among threads, I'm wondering how the {{volatile long}} comes
into play. I agree with your previous comment that the thread local implementation is not
ideal for this use case as the RPC call will generally dominate the total overhead anyway.
If true, an AtomicLong would work just fine.

Do you have any quick comments about this? Thanks.

> 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, 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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