[jira] [Created] (CASSANDRA-6385) FD phi estimator initial conditions

["Quentin Conner (JIRA)" <ji...@apache.org>]

Quentin Conner created CASSANDRA-6385:
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             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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