keep combiner backward compatible with earlier versions of hadoop
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Key: HADOOP-3586
URL: https://issues.apache.org/jira/browse/HADOOP-3586
Project: Hadoop Core
Issue Type: Bug
Reporter: Olga Natkovich
Fix For: 0.18.0
In hadoop 16 and earlier, the combiner was guaranteed to run once and only once
for each map. In 17 this compatibility was slightly broken: the combiner does
not run if a single <K,V> occupies the entire sort buffer. In 18, this is
further changed to where the combiner can be called multiple times on both map
and reduce sides.
This breaks Pig's current implementation of the combiner and it is not easy to
fix in a short period of time.
We would like to ask that for a way for an application to ask for a backward
compatible behavior for some period of time until it can adjust to the new
behavior.
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