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Posted to commits@cassandra.apache.org by "Quentin Conner (JIRA)" <ji...@apache.org> on 2013/11/20 17:53:44 UTC
[jira] [Commented] (CASSANDRA-6385) FD phi estimator initial
conditions
[ https://issues.apache.org/jira/browse/CASSANDRA-6385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13827836#comment-13827836 ]
Quentin Conner commented on CASSANDRA-6385:
-------------------------------------------
breaking out FD phi initial condition to related issue
> 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
>
> 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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