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From "Robert Joseph Evans (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7901) Have Configuration use Read/Write Locks
Date Fri, 09 Dec 2011 23:00:40 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7901?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13166644#comment-13166644

Robert Joseph Evans commented on HADOOP-7901:

I have not measured any contention in the Configuration object.  That is a very good point
I really should not be doing optimizations without measuring first to know if they are needless
or not.  I really should rename this measure lock contention in Configuration object and then
possibly use Read/Write Locks.

This was filed partly in response to MAPREDUCE-3519.  There was a deadlock introduced because
one thread grabbed a lock on a Configuration object and then tried to grab a different lock
while a separate thread tried to grab the locks in reverse order.  This seems especially odd
to me because my gut feeling is that most of the time all we are trying to do is to read data
from Configuration. Very rarely do we want to change it, so I thought that it would be a potential
performance improvement, in addition to removing some of the potential for these deadlocks
in the future.

So before doing any code changes I will measure the level of lock contention.
> Have Configuration use Read/Write Locks
> ---------------------------------------
>                 Key: HADOOP-7901
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7901
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: conf
>    Affects Versions: 0.23.1
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
> We can potentially improve performance by moving to read/write locks for configuration
instead of the current synchronization. 

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