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https://issues.apache.org/jira/browse/HDFS-16233?focusedWorklogId=653914&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-653914
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ASF GitHub Bot logged work on HDFS-16233:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 22/Sep/21 06:11
Start Date: 22/Sep/21 06:11
Worklog Time Spent: 10m
Work Description: jojochuang opened a new pull request #3468:
URL: https://github.com/apache/hadoop/pull/3468
### Description of PR
Async profiler finds the COW of EnumCounters is expensive. Propose a new
implementation to reduce the cost.
### How was this patch tested?
Performance optimization. No functional change so use existing unit tests.
### For code changes:
- [ ] Does the title or this PR starts with the corresponding JIRA issue id
(e.g. 'HADOOP-17799. Your PR title ...')?
- [ ] Object storage: have the integration tests been executed and the
endpoint declared according to the connector-specific documentation?
- [ ] If adding new dependencies to the code, are these dependencies
licensed in a way that is compatible for inclusion under [ASF
2.0](http://www.apache.org/legal/resolved.html#category-a)?
- [ ] If applicable, have you updated the `LICENSE`, `LICENSE-binary`,
`NOTICE-binary` files?
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Issue Time Tracking
-------------------
Worklog Id: (was: 653914)
Remaining Estimate: 0h
Time Spent: 10m
> 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
> Attachments: Screen Shot 2021-09-22 at 1.59.59 PM.png,
> profile_c7_delete_asyncaudit.html
>
> Time Spent: 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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