Ravi Teja Chilukuri created HIVE-16414:
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Summary: [Hive on Tez] Union queries resources efficiency less on
Tez than Mapreduce
Key: HIVE-16414
URL: https://issues.apache.org/jira/browse/HIVE-16414
Project: Hive
Issue Type: Bug
Components: Tez
Affects Versions: 2.1.0
Reporter: Ravi Teja Chilukuri
When a hive union query with the sub queries reading the same table is run in
Mapreduce and tez, Mapreduce reads the table only once, no matter how many
reads on the same table are present,
but tez reads the same table multiple times in the form of multiple vertices.
If a table is to be read by X mappers,
Tez runs with kX map tasks where k is the number of sub queries reading from
the same table and
Mapreduce runs with X mappers no matter how many sub queries are present.
For such union queries, we need to fall back to MR instead of TEZ.
*Query:*
http://pastebin.com/t6n91u6a
*Tez explain plan:*
http://pastebin.com/aWwVxhii
*MR explain plan:*
http://pastebin.com/iDbWwtKR
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