[jira] [Created] (CASSANDRA-6683) BADNESS_THRESHOLD does not working correctly with DynamicEndpointSnitch

["Kirill Bogdanov (JIRA)" <ji...@apache.org>]

Kirill Bogdanov created CASSANDRA-6683:
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             Summary: BADNESS_THRESHOLD does not working correctly with DynamicEndpointSnitch
                 Key: CASSANDRA-6683
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6683
             Project: Cassandra
          Issue Type: Bug
          Components: Core
         Environment: Linux 3.8.0-33-generic
            Reporter: Kirill Bogdanov
             Fix For: 2.0.5


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

Before calling sortByProximityWithScore we comparing each nodes score ratios to the badness threshold.
{code}
if ((first - next) / first >  BADNESS_THRESHOLD)
            {
                sortByProximityWithScore(address, addresses);
                return;
            }
{code}

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:
{code}
if (Math.abs((first - next) / first) > BADNESS_THRESHOLD)
{code}

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

Thanks.
 



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