fix(backend): correct EMA formula in EmaHealthTracker - #26
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The previous implementation used a simple moving average:
new = (old + sample) / 2
This is not a true EMA - it always assigns 50% weight to the most
recent sample regardless of history, causing excessive sensitivity
to latency spikes.
Replace with the standard EMA formula:
new = alpha * sample + (1 - alpha) * old
Add alpha field to HealthConfig (default: 0.1) so callers can tune
the smoothing factor. A lower alpha retains more historical data and
is less sensitive to transient spikes, which is desirable for backend
health tracking in a production RPC proxy.
Update tests to reflect the corrected formula.
Closes refcell#25
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Summary
Fixes #25
EmaHealthTrackerwas computing latency with a simple moving averageinstead of a true exponential moving average.
Changes
alpha: f64field toHealthConfig(default0.1)(old + sample) / 2withalpha * sample + (1 - alpha) * oldBefore / After
(old + sample) / 2alpha * sample + (1-alpha) * oldTesting
All existing tests pass with updated expected values.