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Posted to user@hive.apache.org by prasenjit mukherjee <pr...@gmail.com> on 2010/02/21 04:58:13 UTC

Working/Semantics of REDUCE

I am trying to understand the working of REDUCE operator in hive.  As
mentioned in one of the docs "both MAP and REDUCE are "syntactic
sugar" for the more general select transform" does it mean REDUCE
applies only on the local batch-data ( acting only as "local-reduce"
) or they do act on the entire values for a particular key ? For MAP
command  its ok, as its ok for them to act only on a subset of the
data. But for REDUCE semantics to work it has to act on the entire set
of values for that particular key.

Let me know if I have misunderstood any of the semantics.

-Thanks,
Prasen