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From "Sami Siren (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-387) LocalJobRunner assigns duplicate mapid's
Date Tue, 25 Jul 2006 18:44:14 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-387?page=comments#action_12423405 ] 
            
Sami Siren commented on HADOOP-387:
-----------------------------------

One more note, there were couiple of other places in code where the random was used in the
same way, perhaps someone with better understanding of the internals should check them out
too.

> LocalJobRunner assigns duplicate mapid's
> ----------------------------------------
>
>                 Key: HADOOP-387
>                 URL: http://issues.apache.org/jira/browse/HADOOP-387
>             Project: Hadoop
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.4.0
>         Environment: xp, cygwin, jdk1.4.2_12
>            Reporter: Sami Siren
>         Attachments: hadoop-fix-dup-id-0.4.patch, hadoop-fix-dup-id-trunk.patch
>
>
> While hunting down nutch issue NUTCH-266 i discovered that id's are generated with following
fragment of code:
>     private String newId() {
>       return Integer.toString(Math.abs(new Random().nextInt()),36);
>     }
> and the related Javadoc:
> "
> public Random()
>     Creates a new random number generator. Its seed is initialized to a value based on
the current time:
>          public Random() { this(System.currentTimeMillis()); }
>     Two Random objects created within the same millisecond will have the same sequence
of random numbers.
> "
> it appears that in this case there are more than one Random pobject generated at the
same millisecond and id's are
> no longer unique.

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