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Date: Wed, 20 Nov 2013 22:55:36 +0000 (UTC)
From: "Brandon Williams (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (CASSANDRA-6385) FD phi estimator initial
 conditions
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    [ https://issues.apache.org/jira/browse/CASSANDRA-6385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13828246#comment-13828246 ] 

Brandon Williams commented on CASSANDRA-6385:
---------------------------------------------

+1

> FD phi estimator initial conditions
> -----------------------------------
>
>                 Key: CASSANDRA-6385
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6385
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Quentin Conner
>            Assignee: Jonathan Ellis
>            Priority: Minor
>             Fix For: 1.2.13, 2.0.3
>
>         Attachments: 6385-v2.txt, 6385-v3.txt, 6385.txt, 6835-v4.txt
>
>
> phi estimates are calculated for newly discovered nodes from an un-filled (new, uninitialized) deque.
> The inter-arrival time (elapsed time between gossip heartbeats) is stored in the o.a.c.gms.ArrivalWindow.arrivalIntervale deque for each received heartbeat, up to the maximum window size of 1000 samples.
> In the o.a.c.gms.FailureDetector.interpret() method, phi is calculated for the node which uses a statistical measure called variance.  Like mean, variance on a population (a set of numbers or measurements) is not statistically relevant unless the population set size is 30 or greater. 
> When a new node is discovered, the calculated variance is higher than normal, and causes phi to be higher than normal, resulting in a false positive failure detection.


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