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https://issues.apache.org/jira/browse/HBASE-3996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13240632#comment-13240632
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Todd Lipcon commented on HBASE-3996:
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bq. hbase jar on job tracker is updated to include the versioning mechanism but
the job client has pre-versioning hbase jar.
The jar on the JT doesn't matter. Split computation and interpretation happens
only in the user code -- i.e on the client machine and inside the tasks
themselves. So you don't need HBase installed on the JT at all. As for the TTs,
it's possible to configure the TTs to put an hbase jar on the classpath, but I
usually recommend against it for the exact reason you're mentioning - if the
jars differ in version, and they're not 100% API compatible, you can get nasty
errors. The recommended deployment is to _not_ put hbase on the TT classpath,
and instead ship the HBase dependencies as part of the MR job, using the
provided utility function in TableMapReduceUtil.
> Support multiple tables and scanners as input to the mapper in map/reduce jobs
> ------------------------------------------------------------------------------
>
> Key: HBASE-3996
> URL: https://issues.apache.org/jira/browse/HBASE-3996
> Project: HBase
> Issue Type: Improvement
> Components: mapreduce
> Reporter: Eran Kutner
> Assignee: Eran Kutner
> Fix For: 0.96.0
>
> Attachments: 3996-v2.txt, 3996-v3.txt, 3996-v4.txt, 3996-v5.txt,
> 3996-v6.txt, 3996-v7.txt, HBase-3996.patch
>
>
> It seems that in many cases feeding data from multiple tables or multiple
> scanners on a single table can save a lot of time when running map/reduce
> jobs.
> I propose a new MultiTableInputFormat class that would allow doing this.
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