Struct PhiAccrualFailureDetector

pub(crate) struct PhiAccrualFailureDetector {
    threshold: f32,
    min_std_deviation_millis: f32,
    acceptable_heartbeat_pause_millis: u32,
    first_heartbeat_estimate_millis: u32,
    heartbeat_history: HeartbeatHistory,
    last_heartbeat_millis: Option<i64>,
}

This is our port of Akka’s “PhiAccrualFailureDetector” under Apache License 2.0.

You can find it’s document here: https://doc.akka.io/docs/akka/2.6.21/typed/failure-detector.html

Implementation of ‘The Phi Accrual Failure Detector’ by Hayashibara et al. as defined in their paper: https://oneofus.la/have-emacs-will-hack/files/HDY04.pdf

The suspicion level of failure is given by a value called φ (phi). The basic idea of the φ failure detector is to express the value of φ on a scale that is dynamically adjusted to reflect current network conditions. A configurable threshold is used to decide if φ is considered to be a failure.

The value of φ is calculated as:

φ = -log10(1 - F(timeSinceLastHeartbeat)

where F is the cumulative distribution function of a normal distribution with mean and standard deviation estimated from historical heartbeat inter-arrival times.

Fields

threshold: f32

A low threshold is prone to generate many wrong suspicions but ensures a quick detection in the event of a real crash. Conversely, a high threshold generates fewer mistakes but needs more time to detect actual crashes.

min_std_deviation_millis: f32

Minimum standard deviation to use for the normal distribution used when calculating phi. Too low standard deviation might result in too much sensitivity for sudden, but normal, deviations in heartbeat inter arrival times.

acceptable_heartbeat_pause_millis: u32

Duration corresponding to number of potentially lost/delayed heartbeats that will be accepted before considering it to be an anomaly. This margin is important to be able to survive sudden, occasional, pauses in heartbeat arrivals, due to for example network drop.

first_heartbeat_estimate_millis: u32

Bootstrap the stats with heartbeats that corresponds to this duration, with a rather high standard deviation (since environment is unknown in the beginning).

heartbeat_history: HeartbeatHistory

last_heartbeat_millis: Option<i64>

Implementations

impl PhiAccrualFailureDetector

pub(crate) fn from_options(options: PhiAccrualFailureDetectorOptions) -> Self

pub(crate) fn heartbeat(&mut self, ts_millis: i64)

pub(crate) fn is_available(&self, ts_millis: i64) -> bool

pub(crate) fn phi(&self, ts_millis: i64) -> f64

The suspicion level of the accrual failure detector.

If a connection does not have any records in failure detector then it is considered healthy.

Trait Implementations

impl Default for PhiAccrualFailureDetector

fn default() -> Self

Returns the “default value” for a type.