[MAPREDUCE-5979] FairScheduler: zero weight can cause sort failures

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.2.1
• Fix Version/s: 1.3.0
• Component/s: scheduler
• Hadoop Flags: Reviewed
• Assignee: Anubhav Dhoot
• Reporter: Anubhav Dhoot
• Created: 17/Jul/14 23:09
• Updated: 22/Jul/14 23:04
• Resolved: 22/Jul/14 23:04

Description

When the weight is set to zero (which is possible with a custom weight adjuster) we can get failures in comparing schedulables.
This is because when calculating running tasks to weight ratio could result in a 0.0/0.0 which ends up as NaN. Comparisons with NaN are undefined such that (int)Math.signum(NaN - anyNumber) will be 0 causing different criteria to be used in comparison which may not be consistent. This will result in
IllegalArgumentException: Comparison method violates its general contract!