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fix: cherry picker weighted latency formula #901

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fix: cherry picker weighted latency formula #901

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62c7243
Implemented suggested changes from discord user msa6867#1823
blockjoe Jul 21, 2022
61b35a5
tests: update weighted latency result
crisog Jul 22, 2022
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11 changes: 8 additions & 3 deletions src/services/cherry-picker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,11 @@ const EXPECTED_SUCCESS_LATENCY = 0.15
// This multiplier is tested to produce a curve that adequately punishes slow nodes
const WEIGHT_MULTIPLIER = 35

// This weight controls how much weight is given to the p90 service quality result.
// 1 - this value determines the median service quality weight
// This weights the nodes better than a simple average
const P90_WEIGHT = 0.3

export class CherryPicker {
checkDebug: boolean
redis: Redis
Expand Down Expand Up @@ -258,8 +263,8 @@ export class CherryPicker {
// Don't use weighting until there have been at least 20 requests
if (totalResults > 20) {
serviceQuality.weightedSuccessLatency = (
bucketedServiceQuality.median +
0.3 * bucketedServiceQuality.p90
(1 - P90_WEIGHT) * bucketedServiceQuality.median +
P90_WEIGHT * bucketedServiceQuality.p90
).toFixed(5)
}
serviceQuality.metadata = {
Expand Down Expand Up @@ -398,7 +403,7 @@ export class CherryPicker {
let benchmark = previousNodeLatency

// Only count the latency difference if this node is slower than the expected success latency
if (previousNodeLatency > 0 && sortedLog.medianSuccessLatency > EXPECTED_SUCCESS_LATENCY) {
if (previousNodeLatency > 0 && sortedLog.weightedSuccessLatency > EXPECTED_SUCCESS_LATENCY) {
// If previous node latency is faster than expected success, use the expected as the benchmark
if (previousNodeLatency < EXPECTED_SUCCESS_LATENCY) {
benchmark = EXPECTED_SUCCESS_LATENCY
Expand Down
2 changes: 1 addition & 1 deletion tests/unit/cherry-picker.unit.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -275,7 +275,7 @@ describe('Cherry picker service (unit)', () => {
const session = await new PocketMock().object().getNewSession(undefined)
const expectedLogs = JSON.stringify({
medianSuccessLatency: '0.25000',
weightedSuccessLatency: '0.32860', // average after calculation from fn
weightedSuccessLatency: '0.25360', // average after calculation from fn
results: {
'200': 25,
'500': 2,
Expand Down