Struct PeakEWMA 

pub struct PeakEWMA {
    pub decay: f64,
    pub rtt: f64,
    pub last_event: Instant,
}

exponentially weighted moving average with high sensibility to latency bursts

It reads no clock: construction, Self::observe and Self::get each take the instant they happen at, so the decay a simulator observes is a function of the instants it supplies (#1684).

cf Finagle for the original implementation: https://github.com/twitter/finagle/blob/9cc08d15216497bb03a1cafda96b7266cfbbcff1/finagle-core/src/main/scala/com/twitter/finagle/loadbalancer/PeakEwma.scala

Fields

decay: f64

decay in nanoseconds

higher values will make the EWMA decay slowly to 0

rtt: f64

estimated RTT in nanoseconds

must be set to a high enough default value so that new backends do not get all the traffic right away

last_event: Instant

last modification

Implementations

impl PeakEWMA

pub fn new(now: Instant) -> Self

A fresh average created at now, which the first decay is measured from. Hardcoded default values for now.

pub fn observe(&mut self, rtt: f64, now: Instant)

Fold an observed rtt (in nanoseconds) made at now into the average.

An instant earlier than the last event decays nothing: the elapsed time saturates at zero.

pub fn get(&mut self, active_requests: usize, now: Instant) -> f64

The cost of a backend with active_requests in flight, as seen at now.

Trait Implementations

impl Clone for PeakEWMA

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PeakEWMA

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for PeakEWMA

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for PeakEWMA