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https://issues.apache.org/jira/browse/HADOOP-1017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473791
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Doug Cutting commented on HADOOP-1017:
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A few more thoughts:
- should constructorCache be 'static final', and hence named CACHE, all-caps?
- the values of the WeakHashMap are of type Constructor, each which references
its Class, the key. According to
http://java.sun.com/j2se/1.5.0/docs/api/java/util/WeakHashMap.html, if values
reference the keys, entries will never by collected. So we should either just
use a HashMap, and not permit these to be collected, which is probably fine, or
change the values to be WeakReferences to the constructors.
> 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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