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From "Tyler Hobbs (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-6683) BADNESS_THRESHOLD does not working correctly with DynamicEndpointSnitch
Date Wed, 12 Feb 2014 16:58:31 GMT


Tyler Hobbs commented on CASSANDRA-6683:

[~brandon.williams] was our motivation for not calling {{sortByProximityWithScore}} every
time just the overhead of that operation? It seems like it shouldn't have a large impact unless
the RF is high.  If we want to handle the high-RF case more efficiently, perhaps we could
add a parameter that specifies how many of the replicas will be used (based on the consistency
level) and just move the N lowest scores to the front if the first N scores aren't within

> BADNESS_THRESHOLD does not working correctly with DynamicEndpointSnitch
> -----------------------------------------------------------------------
>                 Key: CASSANDRA-6683
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>         Environment: Linux 3.8.0-33-generic
>            Reporter: Kirill Bogdanov
>              Labels: snitch
>             Fix For: 2.0.6
> There is a problem in ** in sortByProximityWithBadness()
> Before calling sortByProximityWithScore we comparing each nodes score ratios to the badness
> {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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