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From "Gera Shegalov (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-12107) long running apps may have a huge number of StatisticsData instances under FileSystem
Date Tue, 23 Jun 2015 21:27:43 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-12107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14598397#comment-14598397
] 

Gera Shegalov commented on HADOOP-12107:
----------------------------------------

Thanks for v3 [~sjlee0]! 

*FileSystem.java:*

*{{getThreadStatistics}}:*
Minimize the code executed under the monitor. Pull reference creation out of {{synchronized}}
similar to what it was before. Note that currentThread is a native call.


*{{Cleaner#run}}*
Catch and log InterruptedException in the while loop, such that thread does not die on a spurious
wakeup. It's safe since it's a daemon thread.

Nits:
can we be more specific in the naming, to the tune of: STATS_DATA_CLEANER, STATS_DATA_REFQUEUE,
StatsDataCleaner. 

*{{testStatisticsThreadLocalDataCleanUp}}*
Since the test uses waits, pass some reasonable timeout to {{@Test}}

make 'int size' and 'int maxSeconds' final. 

> 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: Minor
>         Attachments: HADOOP-12107.001.patch, HADOOP-12107.002.patch, HADOOP-12107.003.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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