Improve feed throttler and tests

2 files changed, 28 insertions, 4 deletions

diff --git a/client/go/internal/vespa/document/throttler.go b/client/go/internal/vespa/document/throttler.go
index 0400ba1a150..3eb0ccd17f6 100644
--- a/client/go/internal/vespa/document/throttler.go
+++ b/client/go/internal/vespa/document/throttler.go
@@ -73,8 +73,12 @@ func (t *dynamicThrottler) Sent() {
 	t.throughputs[index] = currentThroughput
 
 	// Loop over throughput measurements and pick the one which optimises throughput and latency.
-	choice := float64(currentInflight)
+	best := float64(currentInflight)
 	maxObjective := float64(-1)
+	choice := 0
+	j := -1
+	k := -1
+	s := 0.0
 	for i := len(t.throughputs) - 1; i >= 0; i-- {
 		if t.throughputs[i] == 0 {
 			continue // Skip unknown values
@@ -83,10 +87,25 @@ func (t *dynamicThrottler) Sent() {
 		objective := t.throughputs[i] * math.Pow(inflight, throttlerWeight-1) // Optimise throughput (weight), but also latency (1 - weight)
 		if objective > maxObjective {
 			maxObjective = objective
-			choice = inflight
+			best = inflight
+			choice = i
 		}
+		// Additionally, smooth the throughput values, to reduce the impact of noise, and reduce jumpiness
+		if j != -1 {
+			u := t.throughputs[j]
+			if k != -1 {
+				t.throughputs[j] = (2*u + t.throughputs[i] + s) / 4
+			}
+			s = u
+		}
+		k = j
+		j = i
+	}
+	target := int64((rand.Float64()*0.40+0.84)*best + rand.Float64()*4 - 1) // Random walk, skewed towards increase
+	// If the best inflight is at the high end of the known, we override the random walk to speed up upwards exploration
+	if choice == j && choice+1 < len(t.throughputs) {
+		target = int64(1 + float64(t.minInflight)*math.Pow(256, (float64(choice)+1.5)/float64(len(t.throughputs))))
 	}
-	target := int64((rand.Float64()*0.20 + 0.92) * choice) // Random walk, skewed towards increase
 	t.targetInflight.Store(max(t.minInflight, min(t.maxInflight, target)))
 }
 
diff --git a/client/go/internal/vespa/document/throttler_test.go b/client/go/internal/vespa/document/throttler_test.go
index 410e518e596..b386e0d5105 100644
--- a/client/go/internal/vespa/document/throttler_test.go
+++ b/client/go/internal/vespa/document/throttler_test.go
@@ -9,11 +9,16 @@ import (
 func TestThrottler(t *testing.T) {
 	clock := &manualClock{tick: time.Second}
 	tr := newThrottler(8, clock.now)
+
 	if got, want := tr.TargetInflight(), int64(16); got != want {
 		t.Errorf("got TargetInflight() = %d, but want %d", got, want)
 	}
-	for tr.TargetInflight() < int64(18) {
+	for i := 0; i < 30; i++ {
 		tr.Sent()
+		tr.Success()
+	}
+	if got, want := tr.TargetInflight(), int64(18); got != want {
+		t.Errorf("got TargetInflight() = %d, but want %d", got, want)
 	}
 	tr.Throttled(34)
 	if got, want := tr.TargetInflight(), int64(17); got != want {