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https://issues.apache.org/jira/browse/HADOOP-12107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14606431#comment-14606431
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Gera Shegalov commented on HADOOP-12107:
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bq. You could make the same argument to stop development on almost any patch.
I disagree with such a strong statement. It's not the case in my experience.
Thanks for pointing out the compatibility document. It gives us a formal basis
to go on, and not delay [~sjlee0]'s important fix. Maybe one day we'll have a
compatibility test suite based on that doc.
bq. It's simply unreasonable to try to support users who are putting their code
inside the org.apache.hadoop.fs
We develop new Hadoop features and often they do not make it upstream
immediately. It happens that we have classes in their intended packages but we
can deal with this. We are not affected by this particular change, either.
+1 for both trunk and branch 2. [~mingma], do you want to exercise your
committer rights :) ?
> 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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