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From "Quentin Conner (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-6385) FD phi estimator initial conditions
Date Wed, 20 Nov 2013 16:51:35 GMT
Quentin Conner created CASSANDRA-6385:
-----------------------------------------

             Summary: 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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