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Phi Accrual Failure Detector

Phi Accrual Failure Detector keeps track of the intervals between heartbeats in a sliding window of time and measures the mean and variance of these samples and calculates a value of suspicion level (Phi). The value of phi increases when the period since the last heartbeat gets longer. If the network becomes slow or unreliable, the resulting mean and variance increase, there needs to be a longer period for which no heartbeat is received before the member is suspected.

The following is an example configuration with property descriptions.

  • XML

  • YAML

  • Java Member API

        <property name="hazelcast.heartbeat.failuredetector.type">phi-accrual</property> (1)
        <property name="hazelcast.heartbeat.interval.seconds">1</property> (2)
        <property name="hazelcast.max.no.heartbeat.seconds">60</property> (3)
        <property name="hazelcast.heartbeat.phiaccrual.failuredetector.threshold">10</property> (4)
        <property name="hazelcast.heartbeat.phiaccrual.failuredetector.sample.size">200</property> (5)
        <property name="hazelcast.heartbeat.phiaccrual.failuredetector.min.std.dev.millis">100</property> (6)
    hazelcast.heartbeat.failuredetector.type: phi-accrual (1)
    hazelcast.heartbeat.interval.seconds: 1 (2)
    hazelcast.max.no.heartbeat.seconds: 60 (3)
    hazelcast.heartbeat.phiaccrual.failuredetector.threshold: 10 (4)
    hazelcast.heartbeat.phiaccrual.failuredetector.sample.size: 200 (5)
    hazelcast.heartbeat.phiaccrual.failuredetector.min.std.dev.millis: 100 (6)
Config config = ...;
config.setProperty("hazelcast.heartbeat.failuredetector.type", "phi-accrual"); (1)
config.setProperty("hazelcast.heartbeat.interval.seconds", "1"); (2)
config.setProperty("hazelcast.max.no.heartbeat.seconds", "60"); (3)
config.setProperty("hazelcast.heartbeat.phiaccrual.failuredetector.threshold", "10"); (4)
config.setProperty("hazelcast.heartbeat.phiaccrual.failuredetector.sample.size", "200"); (5)
config.setProperty("hazelcast.heartbeat.phiaccrual.failuredetector.min.std.dev.millis", "100"); (6)
1 The value must be phi-accrual.
2 Interval at which member heartbeat messages are sent to each other.
3 Timeout that defines when a cluster member is suspect because it has not sent any heartbeats. As Phi Accrual Failure Detector is adaptive to network conditions, you can define a lower hazelcast.max.no.heartbeat.seconds than defined in the Deadline Failure Detector timeout. For further information on the Deadline Failure Detector timeout, see the timeout topic.
4 The phi threshold at which a member is considered unreachable and marked as suspect. After calculated phi exceeds this threshold, a member is considered as unreachable and marked as suspected. A low threshold threshold allows you to detect any crashes or failures in a member, but can generate more failures and cause the wrong member to be marked as suspect. A higher threshold generates fewer failures but is slower to detect actual crashes/failures. If you set phi = 1, the possibility of an incorrectly-identified failure is around 10%. If you set phi = 2, this falls to around 1%, and setting phi = 3 reduces this further to around 0.1%. The likelihood of incorrectly-identified failures continues to reduce in this way as you increase the value. By default, the phi threshold is set to 10.
5 Number of samples to retain for history. By default, this is set to 200.
6 Minimum standard deviation for phi calculations in a normal distribution.
If you set the standard deviation too low, this can result in excessive sensitivity.