[MAPREDUCE-5211] Reducer intermediate files can collide during merge

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 0.23.7
• Fix Version/s: 0.23.8
• Component/s: mrv2
• Labels: 2.0.4.2
• Target Version/s: 2.1.0-beta, 0.23.8
• Hadoop Flags: Reviewed
• Assignee: Jason Darrell Lowe
• Reporter: Jason Darrell Lowe
• Created: 06/May/13 18:32
• Updated: 16/Jun/13 12:25
• Resolved: 16/Jun/13 12:25

Description

The OnDiskMerger.merge method constructs an output path that is not unique to a reduce attempt, and as a result can result in a file collision with other reducers from the same app that are running on the same node. In addition the name of the output file is based on MapOutput.toString which may not be unique in light of multi-pass merges on disk since the mapId will be null and the basename ends up as "MapOutput(null, DISK)"

Issue Links

• is broken by: MAPREDUCE-3685 There are some bugs in implementation of MergeManager