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MapReduce >> mail # user >> Data locality of map-side join


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Data locality of map-side join
Hi guys,

I've been trying to figure out whether a map-side join using the
join-package does anything clever regarding data locality with respect
to at least one of the partitions to join. To be more specific, if I
want to join two datasets and some partition of dataset A is larger than
the corresponding partition of dataset B, does Hadoop account for this
and try to ensure that the map task is executed on the datanode storing
the bigger partition thus reducing data transfer (if the other partition
does not happen to be located on that same datanode)? I couldn't
conclude the one or the other behavior from the source code and I
couldn't find any documentation about this detail.

Thanks for clarifying!
Sigurd