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https://issues.apache.org/jira/browse/CASSANDRA-2597?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis updated CASSANDRA-2597:
--------------------------------------
Component/s: (was: Contrib)
Core
Fix Version/s: (was: 0.7.6)
0.7.7
> inconsistent implementation of 'cumulative distribution function' for
> Exponential Distribution
> ----------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-2597
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2597
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Jonathan Ellis
> Assignee: paul cannon
> Priority: Minor
> Fix For: 0.7.7
>
>
> As reported on the mailing list
> (http://mail-archives.apache.org/mod_mbox/cassandra-dev/201104.mbox/%[email protected]%3E),
> {quote}
> I just found there are two implementations of 'cumulative distribution
> function' for Exponential Distribution and there are inconsistent :
> *FailureDetector*
> {code:java}
> org.apache.cassandra.gms.ArrivalWindow.p(double)
> double p(double t)
> {
> double mean = mean();
> double exponent = (-1)*(t)/mean;
> return *Math.pow(Math.E, exponent)*;
> }
> {code}
> *DynamicEndpointSnitch*
> {code:java}
> org.apache.cassandra.locator.AdaptiveLatencyTracker.p(double)
> double p(double t)
> {
> double mean = mean();
> double exponent = (-1) * (t) / mean;
> return *1 - Math.pow( Math.E, exponent);*
> }
> {code}
> According to the Exponential Distribution cumulative distribution function
> definition<http://en.wikipedia.org/wiki/Exponential_distribution#Cumulative_distribution_function>,
> the later one is correct
> {quote}
> ... however FailureDetector has been working as advertised for some time now.
> Does this mean the Snitch version is actually wrong?
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