[
https://issues.apache.org/jira/browse/CASSANDRA-2597?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Ryan King updated CASSANDRA-2597:
---------------------------------
Component/s: (was: Core)
Contrib
Description:
As reported on the mailing list
(http://mail-archives.apache.org/mod_mbox/cassandra-dev/201104.mbox/%3CAANLkTimdMSLE8-z0x+0kvzqp7za3AEMLaOFXvd4Z=t...@mail.gmail.com%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?
was:
As reported on the mailing list
(http://mail-archives.apache.org/mod_mbox/cassandra-dev/201104.mbox/%3CAANLkTimdMSLE8-z0x+0kvzqp7za3AEMLaOFXvd4Z=t...@mail.gmail.com%3E),
{quote}
I just found there are two implementations of 'cumulative distribution
function' for Exponential Distribution and there are inconsistent :
*FailureDetector*
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)*;
}
*DynamicEndpointSnitch*
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);*
}
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?
Fix Version/s: (was: 0.7.7)
0.7.6
> 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: Contrib
> Reporter: Jonathan Ellis
> Assignee: paul cannon
> Priority: Minor
> Fix For: 0.7.6
>
>
> As reported on the mailing list
> (http://mail-archives.apache.org/mod_mbox/cassandra-dev/201104.mbox/%3CAANLkTimdMSLE8-z0x+0kvzqp7za3AEMLaOFXvd4Z=t...@mail.gmail.com%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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