perf: reuse reverse proxy candidate slices

reverseproxy.go

@@ -91,6 +91,13 @@ var reverseProxyCopyBufferPool = sync.Pool{
 	},
 }
 
+var reverseProxyCandidatePool = sync.Pool{
+	New: func() any {
+		s := make([]*reverseProxyUpstream, 0, 8)
+		return &s
+	},
+}
+
 type reverseProxyStatusError struct {
 	status int
 	err    error

reverseproxy_benchmark_test.go

@@ -110,10 +110,10 @@ func BenchmarkReverseProxyCopyResponse(b *testing.B) {
 func BenchmarkReverseProxyAvailableUpstreams(b *testing.B) {
 	proxy := &reverseProxyHandler{
 		upstreams: []*reverseProxyUpstream{
-			{key: "a"},
-			{key: "b"},
-			{key: "c"},
-			{key: "d"},
+			{key: "a", index: 0},
+			{key: "b", index: 1},
+			{key: "c", index: 2},
+			{key: "d", index: 3},
 		},
 		config: ReverseProxyConfig{
 			PassiveHealth: ReverseProxyPassiveHealthConfig{
@@ -135,6 +135,38 @@ func BenchmarkReverseProxyAvailableUpstreams(b *testing.B) {
 	}
 }
 
+func BenchmarkReverseProxySelectUpstream(b *testing.B) {
+	proxy := &reverseProxyHandler{
+		upstreams: []*reverseProxyUpstream{
+			{key: "a", index: 0},
+			{key: "b", index: 1},
+			{key: "c", index: 2},
+			{key: "d", index: 3},
+		},
+		config: ReverseProxyConfig{
+			LoadBalancing: ReverseProxyLoadBalancingConfig{Policy: LBRoundRobin()},
+			PassiveHealth: ReverseProxyPassiveHealthConfig{
+				FailDuration: time.Minute,
+				MaxFails:     3,
+			},
+		},
+	}
+	proxy.upstreams[0].failures = []time.Time{time.Now().Add(-30 * time.Second)}
+
+	c, _ := CreateTestContext(nil)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		selected, err := proxy.selectUpstream(c, nil)
+		if err != nil {
+			b.Fatalf("selectUpstream failed: %v", err)
+		}
+		benchmarkReverseProxySink = selected.index
+	}
+}
+
 func TestReverseProxyCopyResponseWithoutBufferPool(t *testing.T) {
 	proxy := newReverseProxyHandler(ReverseProxyConfig{})
 	dst := newBenchmarkResponseWriter()
@@ -203,4 +235,29 @@ func TestReverseProxyCopyResponseRespectsCustomBufferLength(t *testing.T) {
 	}
 }
 
+func TestReverseProxyAvailableUpstreamsFiltersExcludedAndUnhealthy(t *testing.T) {
+	now := time.Now()
+	proxy := &reverseProxyHandler{
+		upstreams: []*reverseProxyUpstream{
+			{key: "a"},
+			{key: "b", failures: []time.Time{now.Add(-20 * time.Second), now.Add(-10 * time.Second)}},
+			{key: "c"},
+		},
+		config: ReverseProxyConfig{
+			PassiveHealth: ReverseProxyPassiveHealthConfig{
+				FailDuration: time.Minute,
+				MaxFails:     2,
+			},
+		},
+	}
+
+	available := proxy.availableUpstreams(now, map[string]struct{}{"c": {}})
+	if len(available) != 1 {
+		t.Fatalf("expected only one available upstream, got %d", len(available))
+	}
+	if available[0].key != "a" {
+		t.Fatalf("expected upstream 'a', got %q", available[0].key)
+	}
+}
+
 var _ io.Writer = (*benchmarkResponseWriter)(nil)

reverseproxy_lb.go

@@ -137,18 +137,32 @@ func validateReverseProxyLBPolicy(policy ReverseProxyLBPolicy) error {
 func (p *reverseProxyHandler) selectUpstream(c *Context, excluded map[string]struct{}) (*reverseProxyUpstream, error) {
 	now := time.Now()
 	policy := p.config.LoadBalancing.Policy
-	candidates := p.availableUpstreams(now, excluded)
+	candidateBuf := reverseProxyCandidatePool.Get().(*[]*reverseProxyUpstream)
+	candidates := p.availableUpstreamsInto(now, excluded, *candidateBuf)
 	if len(candidates) == 0 && len(excluded) > 0 {
-		candidates = p.availableUpstreams(now, nil)
+		candidates = p.availableUpstreamsInto(now, nil, candidates[:0])
 	}
 	if len(candidates) == 0 {
+		*candidateBuf = candidates[:0]
+		reverseProxyCandidatePool.Put(candidateBuf)
 		return nil, errReverseProxyNoAvailableUpstreams
 	}
-	return p.selectUpstreamWithPolicy(c, candidates, policy), nil
+	selected := p.selectUpstreamWithPolicy(c, candidates, policy)
+	*candidateBuf = candidates[:0]
+	reverseProxyCandidatePool.Put(candidateBuf)
+	return selected, nil
 }
 
 func (p *reverseProxyHandler) availableUpstreams(now time.Time, excluded map[string]struct{}) []*reverseProxyUpstream {
-	candidates := make([]*reverseProxyUpstream, 0, len(p.upstreams))
+	return p.availableUpstreamsInto(now, excluded, nil)
+}
+
+func (p *reverseProxyHandler) availableUpstreamsInto(now time.Time, excluded map[string]struct{}, candidates []*reverseProxyUpstream) []*reverseProxyUpstream {
+	if cap(candidates) < len(p.upstreams) {
+		candidates = make([]*reverseProxyUpstream, 0, len(p.upstreams))
+	} else {
+		candidates = candidates[:0]
+	}
 	for _, upstream := range p.upstreams {
 		if _, skip := excluded[upstream.key]; skip {
 			continue