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https://issues.apache.org/jira/browse/HADOOP-1017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473794
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Ron Bodkin commented on HADOOP-1017:
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How about using a concurrent map if one is available (on Java 5+ or if the
concurrent backport is on the classpath), but falling back to a synchronized
map if one is not? I've implemented code like that before (in our environment
we run single threaded Hadoop jobs so I wasn't aware of the need for thread
safety).
You are right about the values having a reference back to the Class -I think
making the map just a HashMap is probably the right approach, since in most
programs there would be only a handful and the classes won't need to be gc'd
anyhow. it would be possible to make the values SoftReferences instead to allow
collecting Classes but to make the cache less likely to lose useful data.
The cache member certainly could be final and named CACHE, good idea.
> Optimization: Reduce Overhead from ReflectionUtils.newInstance
> --------------------------------------------------------------
>
> Key: HADOOP-1017
> URL: https://issues.apache.org/jira/browse/HADOOP-1017
> Project: Hadoop
> Issue Type: Improvement
> Components: util
> Reporter: Ron Bodkin
> Attachments: cacheCtor.patch, ReflectionUtils.patch.txt,
> TestReflectionUtils.java
>
>
> I found that a significant amount of time on my project was being spent in
> creating constructors for each row of data. I dramatically optimized this
> performance by creating a simple WeakHashMap to cache constructors by class.
> For example, in a sample job I find that ReflectionUtils.newInstance takes
> 200 ms (2% of total) with the cache enabled, but it uses 900 ms (6% of total)
> without the cache.
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