[CASSANDRA-6683] BADNESS_THRESHOLD does not working correctly with DynamicEndpointSnitch

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 2.0.6, 2.1 beta2
• Labels: snitch

Environment

Linux 3.8.0-33-generic

• Severity: Normal
• Assignee: Tom Hobbs
• Reporter: Kirill Bogdanov

Authors

Tom Hobbs

Reviewers

Brandon Williams

• Created: 10/Feb/14 08:11
• Updated: 16/Apr/19 09:31
• Resolved: 25/Feb/14 16:45

Description

There is a problem in DynamicEndpointSnitch.java in sortByProximityWithBadness()

Before calling sortByProximityWithScore we comparing each nodes score ratios to the badness threshold.

if ((first - next) / first >  BADNESS_THRESHOLD)
            {
                sortByProximityWithScore(address, addresses);
                return;
            }

This is not always the correct comparison because first score can be less than next score and in that case we will compare a negative number with positive.

The solution is to compute absolute value of the ratio:

if (Math.abs((first - next) / first) > BADNESS_THRESHOLD)

This issue causing an incorrect sorting of DCs based on their performance and affects performance of the snitch.

Thanks.