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https://issues.apache.org/jira/browse/HBASE-3996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13281995#comment-13281995
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Patrick Yu commented on HBASE-3996:
-----------------------------------
@Ming Ma
I'm not so sure about multi-table inputs, but multi-scan is very useful in
cases where the row keys are prefixed with a salt value in order to avoid the
hot region problem. For example, if the row keys are like byte(0-63) + actual
timestamp, then using one scan with the specific prefix per region (map task)
would be less expensive than using very complicated filters for the same
purpose.
> 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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