[TEZ-3972] Tez DAG can hang when a single task fails to fetch

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.9.1
• Fix Version/s: 0.9.2, 0.10.0
• Assignee: Kuhu Shukla
• Reporter: Kuhu Shukla
• Created: 19/Jul/18 21:18
• Updated: 25/Aug/20 15:00
• Resolved: 18/Sep/18 22:16

Description

Description of the hung DAG:
A DAG with 2 vertices. Map Vertex has 22k maps, downstream vertex Reduce has 1009 tasks. All tasks succeed but one, which hangs. This one task (attempt) is doing a local fetch from a node that (now) has a bad disk. It fails to fetch and reports to the AM for the offending input attempt identifiers. However the AM does not schedule a re-run as uniquefailedOutputReports size is 1 (since only this task attempt failed to fetch) and failure fraction is not met. The denominator for this fraction is the total number of tasks. That causes the re-run to never occur. This JIRA tracks the AM side of the change to alleviate this problem.

Issue Links

• is duplicated by: TEZ-3198 Shuffle failures for the trailing task in a vertex are often fatal to the entire DAG