[jira] [Commented] (HADOOP-11223) Offer a read-only conf alternative to new Configuration()

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-11223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14185364#comment-14185364 ] 

Colin Patrick McCabe commented on HADOOP-11223:
-----------------------------------------------

Interesting idea.  Just to clarify, it seems like there are two separate ideas here:

1. Some kind of read-only wrapper for Configuration, to make it impossible to modify a given configuration object.
2. Avoiding re-reading the XML files more than once.

It seems like #2 could be accomplished pretty easily by having a DefaultConfiguration.java that just had a public static Configuration object.  Then #1 is just a way of making sure that badly behaved programmers don't alter this default configuration when they're using it.  Is that an accurate summary?

+1 for both ideas from me.  I often wish Configuration were an immutable class, perhaps with copy-on-write semantics.  It would eliminate a lot of race conditions.

> Offer a read-only conf alternative to new Configuration()
> ---------------------------------------------------------
>
>                 Key: HADOOP-11223
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11223
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: conf
>            Reporter: Gopal V
>              Labels: Performance
>
> new Configuration() is called from several static blocks across Hadoop.
> This is incredibly inefficient, since each one of those involves primarily XML parsing at a point where the JIT won't be triggered & interpreter mode is essentially forced on the JVM.
> The alternate solution would be to offer a {{Configuration::getDefault()}} alternative which disallows any modifications.
> At the very least, such a method would need to be called from 
> # org.apache.hadoop.io.nativeio.NativeIO::<clinit>()
> # org.apache.hadoop.security.SecurityUtil::<clinit>()
> # org.apache.hadoop.yarn.factory.providers.RecordFactoryProvider::<clinit>



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