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From "Sangjin Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-12107) long running apps may have a huge number of StatisticsData instances under FileSystem
Date Fri, 26 Jun 2015 17:11:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-12107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14603216#comment-14603216
] 

Sangjin Lee commented on HADOOP-12107:
--------------------------------------

FWIW, when I look at the spark code (which may have been the main reason for changes in HADOOP-10688),
it doesn't look like it's using the constructor or the owner member variable: https://github.com/apache/spark/blob/3c0156899dc1ec1f7dfe6d7c8af47fa6dc7d00bf/core/src/main/scala/org/apache/spark/deploy/SparkHadoopUtil.scala

> long running apps may have a huge number of StatisticsData instances under FileSystem
> -------------------------------------------------------------------------------------
>
>                 Key: HADOOP-12107
>                 URL: https://issues.apache.org/jira/browse/HADOOP-12107
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: fs
>    Affects Versions: 2.7.0
>            Reporter: Sangjin Lee
>            Assignee: Sangjin Lee
>            Priority: Critical
>         Attachments: HADOOP-12107.001.patch, HADOOP-12107.002.patch, HADOOP-12107.003.patch,
HADOOP-12107.004.patch, HADOOP-12107.005.patch
>
>
> We observed with some of our apps (non-mapreduce apps that use filesystems) that they
end up accumulating a huge memory footprint coming from {{FileSystem$Statistics$StatisticsData}}
(in the {{allData}} list of {{Statistics}}).
> Although the thread reference from {{StatisticsData}} is a weak reference, and thus can
get cleared once a thread goes away, the actual {{StatisticsData}} instances in the list won't
get cleared until any of these following methods is called on {{Statistics}}:
> - {{getBytesRead()}}
> - {{getBytesWritten()}}
> - {{getReadOps()}}
> - {{getLargeReadOps()}}
> - {{getWriteOps()}}
> - {{toString()}}
> It is quite possible to have an application that interacts with a filesystem but does
not call any of these methods on the {{Statistics}}. If such an application runs for a long
time and has a large amount of thread churn, the memory footprint will grow significantly.
> The current workaround is either to limit the thread churn or to invoke these operations
occasionally to pare down the memory. However, this is still a deficiency with {{FileSystem$Statistics}}
itself in that the memory is controlled only as a side effect of those operations.



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