[MAPREDUCE-7282] MR v2 commit algorithm should be deprecated and not the default

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 3.3.0, 3.2.1, 3.1.3, 3.3.1
• Component/s: mrv2
• Labels: pull-request-available
• Assignee: Unassigned
• Reporter: Steve Loughran
• Created: 01/Jul/20 13:48
• Updated: 06/Jul/21 11:27
• Resolved: 05/Jul/21 20:18

Description

The v2 MR commit algorithm moves files from the task attempt dir into the dest dir on task commit -one by one

It is therefore not atomic

1. if a task commit fails partway through and another task attempt commits -unless exactly the same filenames are used, output of the first attempt may be included in the final result
2. if a worker partitions partway through task commit, and then continues after another attempt has committed, it may partially overwrite the output -even when the filenames are the same

Both MR and spark assume that task commits are atomic. Either they need to consider that this is not the case, we add a way to probe for a committer supporting atomic task commit, and the engines both add handling for task commit failures (probably fail job)

Better: we remove this as the default, maybe also warn when it is being used

Issue Links

• is related to: SPARK-33019 Use spark.hadoop.mapreduce.fileoutputcommitter.algorithm.version=1 by default
• is related to: MAPREDUCE-7300 PathOutputCommitter to add method failedTaskAttemptCommitRecoverable()
• is superceded by: MAPREDUCE-7341 Add a task-manifest output committer for Azure and GCS
• links to: GitHub Pull Request #2349
• links to: https://github.com/apache/hadoop/pull/2349