[MAPREDUCE-460] Should be able to re-run jobs, collecting only missing output

• Type: New Feature
• Status: Reopened
• Priority: Major
• Resolution: Unresolved
• Component/s: mrv2
• Assignee: Unassigned
• Reporter: Bryan Pendleton
• Created: 17/May/06 01:10
• Updated: 18/Jul/14 04:56

Description

For jobs with no side effects (roughly == jobs with speculative execution enabled), if partial output has been generated, it should be possible to re-run the job, and fill in the missing pieces. I have now run the same job twice, once finishing 42 of 44 reduce tasks, another time finishing only 17. Each time, many nodes have failed, causing many many tasks to fail ( in one case, 5k failures from 15k map tasks, 23 failures from 44 reduces), but some valid output was generated. Since the output is only dependent on the input, and both jobs used the same input, I will now be able to combine these two failed task outputs to get a completed job's output. This should be something that can be more automatic.

In particular, it should be possible to resubmit a job, with a list of partitions that should be ignored. A special Combiner, or pre-Combiner, would throw out any map output for partitions that have already been successfully completed, thus reducing the amount of data that needs to be reduced to complete the job. It would, of course, be nice to support "filling in" existing outputs, rather than having to do a move operation on completed outputs.

Issue Links

• is related to: MAPREDUCE-443 snapshot a map-reduce to DFS ... and restore