[HADOOP-4668] Improve JavaDoc on JobConf.setCombinerClass to better document restrictions on combiners

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.20.0
• Component/s: documentation
• Hadoop Flags: Reviewed
• Assignee: Owen O'Malley
• Reporter: Owen O'Malley
• Created: 16/Nov/08 23:17
• Updated: 23/Apr/09 19:17
• Resolved: 21/Nov/08 00:11

Description

It is often not clear to developers that Combiners may be called 0, 1, or many times and that combiners input and output types must be the same and the combiner must not have side effects. Since there isn't a Combiner class, the best place to put this documentation is on JobConf.setCombinerClass.