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https://issues.apache.org/jira/browse/HBASE-2531?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12868935#action_12868935
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Kannan Muthukkaruppan commented on HBASE-2531:
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Writing out the details of one possible solution. Comments welcome.
Old region names continue to have the format:
<tablename>,<startkey>,<timestamp>. For region names in this format, the
encoded name will continue to be the old JenkinsHash implementation.
New region names have the format: <tablename>,<startkey>,<timestamp>,<dirname>
where <dirname> is the md5 hash of the <tablename>,<startkey>,<timestamp> and
will serve as encoded name/directory name in FS for the region.
This preserves the property that child regions (splits) will have a region name
that sorts higher than the parent.
Search to determine what region serves a particular key is done today by
building a key of the form:
<tablename>,<searchkey>,99999999999999
That's 14 9's. On our test cluster I noticed region names of the form:
test1,0013440000,1273816773769. That's 13 digits for the timestamp part. Going
forward, we'll have region names of the form:
test1,<key>,<13digit-ts>,<md5hash>. But the 14 9's based search key would
continue to work just fine even with the new format region names since '9' >
',' .
> 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: 0.21.0
>
>
> 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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