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From Ferdy Galema <ferdy.gal...@kalooga.com>
Subject Re: How to efficiently join HBase tables?
Date Tue, 31 May 2011 12:31:33 GMT
As far as I can tell there is not yet a build-in mechanism you can use 
for this. You could implement your own InputFormat, something like 
MultiTableInputFormat. If you need different map functions for the two 
tables, perhaps something similar to Hadoop's MultipleInputs should do 
the trick.

On 05/31/2011 02:06 PM, Eran Kutner wrote:
> Hi,
> I need to join two HBase tables. The obvious way is to use a M/R job for
> that. The problem is that the few references to that question I found
> recommend pulling one table to the mapper and then do a lookup for the
> referred row in the second table.
> This sounds like a very inefficient way to do  join with map reduce. I
> believe it would be much better to feed the rows of both tables to the
> mapper and let it emit a key based on the join fields. Since all the rows
> with the same join fields values will have the same key the reducer will be
> able to easily generate the result of the join.
> The problem with this is that I couldn't find a way to feed two tables to a
> single map reduce job. I could probably dump the tables to files in a single
> directory and then run the join on the files but that really makes no sense.
> Am I missing something? Any other ideas?
> -eran

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