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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2531) 32-bit encoding of regionnames waaaaaaayyyyy too susceptible to hash clashes
Date Tue, 11 May 2010 18:57:45 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866277#action_12866277
] 

Todd Lipcon commented on HBASE-2531:
------------------------------------

dhruba: I had suggested a similar thing on IRC last night, and people seemed to think that
UUID would be easier to implement. The chances of multiple UUIDs generated in the same nanotime
on the same machine seems pretty small, no?

> 32-bit encoding of regionnames waaaaaaayyyyy too susceptible to hash clashes
> ----------------------------------------------------------------------------
>
>                 Key: HBASE-2531
>                 URL: https://issues.apache.org/jira/browse/HBASE-2531
>             Project: Hadoop HBase
>          Issue Type: Bug
>            Reporter: stack
>            Assignee: stack
>            Priority: Blocker
>             Fix For: 0.20.5, 0.21.0
>
>
> Kannan tripped over two regionnames that hashed the same:
> Here is code demo'ing that his two names hash the same:
> {code}
> package org;
> import org.apache.hadoop.hbase.util.Bytes;
> import org.apache.hadoop.hbase.util.JenkinsHash;
> public class Testing {
>   public static void main(final String [] args) {
>     System.out.println(encodeRegionName(Bytes.toBytes("test1,6838000000,1273541236167")));
>     System.out.println(encodeRegionName(Bytes.toBytes("test1,0520100000,1273541610201")));
>   }
>   /**
>    * @param regionName
>    * @return the encodedName
>    */
>   public static int encodeRegionName(final byte [] regionName) {
>     return Math.abs(JenkinsHash.getInstance().hash(regionName, regionName.length, 0));
>   }
> }
> {code}
> Need new encoding mechanism.  Will need to migrate old regions to new schema.

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