From 930e99485759c4b98f337b1417d6673a451bd436 Mon Sep 17 00:00:00 2001
From: Yingrong Zhao <22300958+VinozzZ@users.noreply.github.com>
Date: Fri, 15 Nov 2024 15:41:01 -0500
Subject: [PATCH] fix: send all traffic through deterministic sampler during
 stress relief activated

---
 collect/collect.go            |  5 ----
 collect/stressRelief.go       | 27 ---------------------
 collect/stress_relief_test.go | 44 -----------------------------------
 3 files changed, 76 deletions(-)

diff --git a/collect/collect.go b/collect/collect.go
index c0efe52f8a..bf6eac6841 100644
--- a/collect/collect.go
+++ b/collect/collect.go
@@ -802,11 +802,6 @@ func (i *InMemCollector) ProcessSpanImmediately(sp *types.Span) (processed bool,
 	_, span := otelutil.StartSpanWith(context.Background(), i.Tracer, "collector.ProcessSpanImmediately", "trace_id", sp.TraceID)
 	defer span.End()
 
-	if !i.StressRelief.ShouldSampleDeterministically(sp.TraceID) {
-		otelutil.AddSpanField(span, "nondeterministic", 1)
-		return false, false
-	}
-
 	var rate uint
 	record, reason, found := i.sampleTraceCache.CheckSpan(sp)
 	if !found {
diff --git a/collect/stressRelief.go b/collect/stressRelief.go
index 76bdea9df3..1b048f37bd 100644
--- a/collect/stressRelief.go
+++ b/collect/stressRelief.go
@@ -27,7 +27,6 @@ type StressReliever interface {
 	Recalc() uint
 	Stressed() bool
 	GetSampleRate(traceID string) (rate uint, keep bool, reason string)
-	ShouldSampleDeterministically(traceID string) bool
 
 	startstop.Starter
 }
@@ -531,29 +530,3 @@ func (s *StressRelief) GetSampleRate(traceID string) (rate uint, keep bool, reas
 	hash := wyhash.Hash([]byte(traceID), hashSeed)
 	return uint(s.sampleRate), hash <= s.upperBound, "stress_relief/deterministic/" + s.reason
 }
-
-// ShouldSampleDeterministically returns true if the trace should be deterministically sampled.
-// It uses the traceID to calculate a hash and then divides it by the maximum possible value
-// to get a percentage. If the percentage is less than the deterministic fraction, it returns true.
-func (s *StressRelief) ShouldSampleDeterministically(traceID string) bool {
-	samplePercentage := s.deterministicFraction()
-	hash := wyhash.Hash([]byte(traceID), hashSeed)
-
-	return float64(hash)/float64(math.MaxUint64)*100 < float64(samplePercentage)
-}
-
-// deterministicFraction returns the fraction of traces that should be deterministic sampled
-// It calculates the result by using the stress level as the fraction between the activation
-// level and 100%. The result is rounded to the nearest integer.
-//
-// for example:
-// - if the stress level is 90 and the activation level is 80, the result will be 50
-// - meaning that 50% of the traces should be deterministic sampled
-func (s *StressRelief) deterministicFraction() uint {
-	if s.overallStressLevel < s.activateLevel {
-		return 0
-	}
-
-	// round to the nearest integer
-	return uint(float64(s.overallStressLevel-s.activateLevel)/float64(100-s.activateLevel)*100 + 0.5)
-}
diff --git a/collect/stress_relief_test.go b/collect/stress_relief_test.go
index 2e88dd5bc8..53660283a8 100644
--- a/collect/stress_relief_test.go
+++ b/collect/stress_relief_test.go
@@ -3,8 +3,6 @@ package collect
 import (
 	"context"
 	"fmt"
-	"math"
-	"math/rand"
 	"testing"
 	"time"
 
@@ -304,48 +302,6 @@ func TestStressRelief_OverallStressLevel_EnableTraceLocality(t *testing.T) {
 	assert.False(t, sr.stressed)
 }
 
-// TestStressRelief_Sample tests that traces are sampled deterministically
-// by traceID.
-// The test generates 10000 traceIDs and checks that the sampling rate is
-// within 10% of the expected value.
-func TestStressRelief_ShouldSampleDeterministically(t *testing.T) {
-	traceCount := 10000
-	traceIDs := make([]string, 0, traceCount)
-	for i := 0; i < traceCount; i++ {
-		traceIDs = append(traceIDs, fmt.Sprintf("%016x%016x", rand.Int63(), rand.Int63()))
-	}
-
-	sr := &StressRelief{
-		overallStressLevel: 90,
-		activateLevel:      60,
-	}
-
-	var sampled int
-	var dropped int
-	var sampledTraceID string
-	var droppedTraceID string
-	for _, traceID := range traceIDs {
-		if sr.ShouldSampleDeterministically(traceID) {
-			sampled++
-			if sampledTraceID == "" {
-				sampledTraceID = traceID
-			}
-		} else {
-			if droppedTraceID == "" {
-				droppedTraceID = traceID
-			}
-			dropped++
-		}
-	}
-
-	difference := float64(sampled)/float64(traceCount)*100 - float64(sr.deterministicFraction())
-	require.LessOrEqual(t, math.Floor(math.Abs(float64(difference))), float64(10), sampled)
-
-	// make sure that the same traceID always gets the same result
-	require.True(t, sr.ShouldSampleDeterministically(sampledTraceID))
-	require.False(t, sr.ShouldSampleDeterministically(droppedTraceID))
-}
-
 func newStressRelief(t *testing.T, clock clockwork.Clock, channel pubsub.PubSub) (*StressRelief, func()) {
 	// Create a new StressRelief object
 	metric := &metrics.MockMetrics{}