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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2629) Class loading quirk prevents inner class method compilation
Date Tue, 28 Jun 2011 22:39:28 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2629?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13056831#comment-13056831
] 

Todd Lipcon commented on MAPREDUCE-2629:
----------------------------------------

Seems reasonable, and thanks for teaching me something new about JVM performance :) Do you
have some benchmark that shows a difference here?

> Class loading quirk prevents inner class method compilation
> -----------------------------------------------------------
>
>                 Key: MAPREDUCE-2629
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2629
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: task
>    Affects Versions: 0.21.0, 0.22.0
>            Reporter: Eric Caspole
>            Priority: Minor
>         Attachments: MAPREDUCE-2629.patch
>
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> While profiling jobs like terasort and gridmix, I noticed that a
> method "org.apache.hadoop.mapreduce.task.ReduceContextImpl.access
> $000" is near the top. It turns out that this is because the
> ReduceContextImpl class has a member backupStore which is accessed
> from an inner class ReduceContextImpl$ValueIterator. Due to the way
> synthetic accessor methods work, every access of backupStore results
> in a call to access$000 to the outer class. For some portion of the
> run, backupStore is null and the BackupStore class has never been
> loaded by the reducer.
> Due to the way the Hotspot JVM inliner works, by default it will not
> inline a short method where the class of of the return value object
> is unloaded - if you use a debug JVM with -XX:+PrintCompilation you
> will see a failure reason message like "unloaded signature classes."
> This causes every call to ReduceContextImpl.access$000 to be executed
> in the interpreter for the handful of bytecodes to return the null
> backupStore.

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