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https://issues.apache.org/jira/browse/HDFS-16233?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17421220#comment-17421220
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Akira Ajisaka commented on HDFS-16233:
--------------------------------------
Backported to branch-3.2.3.
> Do not use exception handler to implement copy-on-write for EnumCounters
> ------------------------------------------------------------------------
>
> Key: HDFS-16233
> URL: https://issues.apache.org/jira/browse/HDFS-16233
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Reporter: Wei-Chiu Chuang
> Assignee: Wei-Chiu Chuang
> Priority: Major
> Labels: pull-request-available
> Fix For: 3.4.0, 2.10.2, 3.2.3, 3.3.2, 3.1.5
>
> Attachments: Screen Shot 2021-09-22 at 1.59.59 PM.png,
> profile_c7_delete_asyncaudit.html
>
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> HDFS-14547 saves the NameNode heap space occupied by EnumCounters by
> essentially implementing a copy-on-write strategy.
> At beginning, all EnumCounters refers to the same ConstEnumCounters to save
> heap space. When it is modified, an exception is thrown and the exception
> handler converts ConstEnumCounters to EnumCounters object and updates it.
> Using exception handler to perform anything more than occasional is bad for
> performance.
> Propose: use instanceof keyword to detect the type of object and do COW
> accordingly.
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