[AURORA-1943] PreemptionVictimFilter does not handle varied ResourceTypes

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.19.0
• Component/s: Scheduler
• Assignee: Bill Farner
• Reporter: Bill Farner
• Created: 29/Jul/17 02:02
• Updated: 08/Nov/17 04:40
• Resolved: 31/Jul/17 13:05

Description

Reported by Mauricio Garavaglia on the dev list:

Hi guys,

There seems to be a bug in this comparator in PreemptionVictimFilter (
https://github.com/apache/aurora/blob/master/src/main/java/org/apache/aurora/scheduler/preemptor/PreemptionVictimFilter.java#L142)
because the comparator doesn’t satisfy transitivity, which is required by
Array.sort's Tim Sort implementation. This fails with a
"java.lang.IllegalArgumentException: Comparison method violates its general
contract!" from time to time.

For example this input of A, B, and C doesn't work in the current
comparator.

A: <1, 1, 1>
B: <2, 2, 2>
C: <0, 2, 1>

Based on the comparator:

B > A
B == C
C == A

Constructs impossible situation where C == B > A == C. As a workaround we
patched to simply sort based on RAM, but anyone have any suggestions about
what a permanent fix for upstream should be? Thanks

A likely culprit is that the filter does not handle comparison of tasks containing different ResourceTypes.

Issue Links

• relates to: AURORA-1949 PreemptionVictimFilterImpl comparator violates transitivity causing exceptions