mapjoin should throw an error if the input is too large
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Key: HIVE-988
URL: https://issues.apache.org/jira/browse/HIVE-988
Project: Hadoop Hive
Issue Type: New Feature
Components: Query Processor
Reporter: Namit Jain
Assignee: Ning Zhang
Fix For: 0.5.0
If the input to the map join is larger than a specific threshold, it may lead
to a very slow execution of the join.
It is better to throw an error, and let the user redo his query as a non
map-join query.
However, the current map-reduce framework will retry the mapper 4 times before
actually killing the job.
Based on a offline discussion with Dhruba, Ning and myself, we came up with the
following algorithm:
Keep a threshold in the mapper for the number of rows to be processed for
map-join. If the number of rows
exceeds that threshold, set a counter and kill that mapper.
The client (ExecDriver) monitors that job continuously - if this counter is
set, it kills the job and also
shows an appropriate error message to the user, so that he can retry the query
without the map join.
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