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https://issues.apache.org/jira/browse/HADOOP-6133?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12728941#action_12728941
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Todd Lipcon commented on HADOOP-6133:
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Owen: the issue with that is that the JobConfigurable.class has to be loaded
through Configuration's ClassLoader. In order to cache it in ReflectionUtils
we'd need to have a Map<ClassLoader, Class> CACHE_JOBCONFIGURABLE_CLASSES as
well. Otherwise we risk having multiple instances of the JobConfigurable.class
and checking isAssignableFrom against the wrong one.
> ReflectionUtils performance regression
> --------------------------------------
>
> Key: HADOOP-6133
> URL: https://issues.apache.org/jira/browse/HADOOP-6133
> Project: Hadoop Common
> Issue Type: Improvement
> Components: conf
> Affects Versions: 0.20.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Attachments: hadoop-6133-0.20.patch, Test.java
>
>
> HADOOP-4187 introduced extra calls to Class.forName in
> ReflectionUtils.setConf. This caused a fairly large performance regression.
> Attached is a microbenchmark that shows the following timings (ms) for 100M
> constructions of new instances:
> Explicit construction (new Test): around ~1.6sec
> Using Test.class.newInstance: around ~2.6sec
> ReflectionUtils on 0.18.3: ~8.0sec
> ReflectionUtils on 0.20.0: ~200sec
> This illustrates the ~80x slowdown caused by HADOOP-4187.
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