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From Igor Tatarinov <i...@decide.com>
Subject single output file per partition?
Date Tue, 20 Aug 2013 21:29:32 GMT
What's the best way to enforce a single output file per partition?

INSERT OVERWRITE TABLE <table>
PARTITION (x,y,z)
SELECT ...
FROM ...
WHERE ...

It tried adding CLUSTER BY x,y,z at the end thinking that sorting will
force a single reducer per partition but that didn't work. I still got
multiple files per partition.

Do I have to use a single reduce task? With a few TB of data that's
probably not a good idea.

My current idea is to create a temp table with the same partitioning
structure. Insert into that table first and then select * from that table
into the output table. With combineinputformat=true that should work right?

Or should I make Hive merge output files instead? (using hive.merge.mapfiles)
Will that work with a partitioned table?

Thanks!
igor

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