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https://issues.apache.org/jira/browse/CASSANDRA-6683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13899375#comment-13899375
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Tyler Hobbs commented on CASSANDRA-6683:
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bq. I'm not sure what you mean exactly, we always end up calling it, we just
don't check badness when it's set to zero.
I was a little confused on my last comment, but let me try again. Right now we
only call {{sortByProximityWithScore()}} if {{BADNESS_THRESHOLD != 0}} and two
neighbors in the list returned by the subsnitch differ by BADNESS_THRESHOLD. I
think it would make more sense (and fix Kirill's case) to always call
{{sortByProximityWithScore()}} and then compare that ordering against the
subsnitch list. Something like this:
{noformat}
defaultOrder = subsnitch.sort(address, addresses);
scoredOrder = sortByProximityWithScore(address, addresses); // make this
return a new list instead of sorting in place
for (int i = 0; i < defaultOrder.size(); i++)
{
if (scores.get(defaultOrder.get(i)) > scores.get(scoredOrder.get(i)) * (1 +
BADNESS_THRESHOLD))
return scoredOrder;
}
return defaultOrder;
{noformat}
bq. Possible, but it'd be a lot of work, because it would change the snitch
interface and we'd still need the old call because not all uses of it have a
consistency level available.
It looks like there aren't too many callers, so it shouldn't be that much work.
I would just make the arg optional and default it to the length of
{{addresses}}.
> 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
> Labels: snitch
> Fix For: 2.0.6
>
>
> 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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