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Date: Fri, 16 Feb 2007 11:11:05 -0800 (PST)
From: "Doug Cutting (JIRA)" <jira@apache.org>
To: hadoop-dev@lucene.apache.org
Subject: [jira] Commented: (HADOOP-1017) Optimization: Reduce Overhead from
 ReflectionUtils.newInstance
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    [ https://issues.apache.org/jira/browse/HADOOP-1017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12473791 ] 

Doug Cutting commented on HADOOP-1017:
--------------------------------------

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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