《互联网产品的服务端架构·规模化与架构演进》9.1 旧链路的问题与基线

// file: internal/feedmig/baseline.go
// tier: L1
// verify: go test ./internal/feedmig/

package feedmig

import "fmt"

// Metric 是一次基线测量得到的三个核心数字。
// 三个字段都用 int64，是因为成本以“分”为单位累计后会很快超过 int32。
type Metric struct {
	LatencyP99Ms int64
	Fanout       int64
	CostCents    int64
}

// Verdict 记录新旧两条链路的对比结论。
// Improved 与 Regressed 里放的是指标名，顺序固定，方便直接写进报告。
type Verdict struct {
	Name      string
	Improved  []string
	Regressed []string
}

// Compare 按固定方向比较两份基线。
// 延迟和成本下降是改善，上升是退化；fanout 上升是退化，下降不自动算改善，
// 因为 fanout 变小也可能意味着有收件人没有被覆盖到。
func Compare(old, new Metric) (Verdict, error) {
	if old.LatencyP99Ms < 0 || old.Fanout < 0 || old.CostCents < 0 ||
		new.LatencyP99Ms < 0 || new.Fanout < 0 || new.CostCents < 0 {
		return Verdict{}, fmt.Errorf(
			"feedmig: metrics must be non-negative, old=%+v new=%+v", old, new)
	}

	v := Verdict{Name: "flat"}
	if new.LatencyP99Ms < old.LatencyP99Ms {
		v.Improved = append(v.Improved, "latency")
	}
	if new.CostCents < old.CostCents {
		v.Improved = append(v.Improved, "cost")
	}
	if new.LatencyP99Ms > old.LatencyP99Ms {
		v.Regressed = append(v.Regressed, "latency")
	}
	if new.CostCents > old.CostCents {
		v.Regressed = append(v.Regressed, "cost")
	}
	if new.Fanout > old.Fanout {
		v.Regressed = append(v.Regressed, "fanout")
	}

	switch {
	case len(v.Improved) > 0 && len(v.Regressed) > 0:
		v.Name = "mixed"
	case len(v.Improved) > 0:
		v.Name = "improved"
	case len(v.Regressed) > 0:
		v.Name = "regressed"
	}
	return v, nil
}

// file: internal/feedmig/baseline_test.go
// tier: L1
// verify: go test ./internal/feedmig/

package feedmig

import (
	"reflect"
	"testing"
)

func TestCompareImproved(t *testing.T) {
	old := Metric{LatencyP99Ms: 420, Fanout: 60, CostCents: 180}
	new := Metric{LatencyP99Ms: 260, Fanout: 40, CostCents: 120}

	got, err := Compare(old, new)
	if err != nil {
		t.Fatalf("Compare: %v", err)
	}
	if got.Name != "improved" {
		t.Fatalf("Name = %q, want improved", got.Name)
	}
	if want := []string{"latency", "cost"}; !reflect.DeepEqual(got.Improved, want) {
		t.Fatalf("Improved = %v, want %v", got.Improved, want)
	}
	if len(got.Regressed) != 0 {
		t.Fatalf("Regressed = %v, want none", got.Regressed)
	}
}

func TestCompareFanoutRegression(t *testing.T) {
	old := Metric{LatencyP99Ms: 300, Fanout: 50, CostCents: 150}
	new := Metric{LatencyP99Ms: 300, Fanout: 80, CostCents: 150}

	got, err := Compare(old, new)
	if err != nil {
		t.Fatalf("Compare: %v", err)
	}
	if got.Name != "regressed" {
		t.Fatalf("Name = %q, want regressed", got.Name)
	}
	if want := []string{"fanout"}; !reflect.DeepEqual(got.Regressed, want) {
		t.Fatalf("Regressed = %v, want %v", got.Regressed, want)
	}
	if len(got.Improved) != 0 {
		t.Fatalf("Improved = %v, want none", got.Improved)
	}
}

func TestCompareMixed(t *testing.T) {
	old := Metric{LatencyP99Ms: 500, Fanout: 40, CostCents: 200}
	new := Metric{LatencyP99Ms: 350, Fanout: 40, CostCents: 260}

	got, err := Compare(old, new)
	if err != nil {
		t.Fatalf("Compare: %v", err)
	}
	if got.Name != "mixed" {
		t.Fatalf("Name = %q, want mixed", got.Name)
	}
	if want := []string{"latency"}; !reflect.DeepEqual(got.Improved, want) {
		t.Fatalf("Improved = %v, want %v", got.Improved, want)
	}
	if want := []string{"cost"}; !reflect.DeepEqual(got.Regressed, want) {
		t.Fatalf("Regressed = %v, want %v", got.Regressed, want)
	}
}

func TestCompareFlat(t *testing.T) {
	m := Metric{LatencyP99Ms: 300, Fanout: 50, CostCents: 150}
	got, err := Compare(m, m)
	if err != nil {
		t.Fatalf("Compare: %v", err)
	}
	if got.Name != "flat" || len(got.Improved) != 0 || len(got.Regressed) != 0 {
		t.Fatalf("got %+v, want flat with no changes", got)
	}

	// fanout 下降不自动算改善：可能只是覆盖变少了。
	lower := m
	lower.Fanout = 20
	got, err = Compare(m, lower)
	if err != nil {
		t.Fatalf("Compare: %v", err)
	}
	if got.Name != "flat" || len(got.Improved) != 0 || len(got.Regressed) != 0 {
		t.Fatalf("fanout decrease should be neutral, got %+v", got)
	}
}

func TestCompareRejectsNegative(t *testing.T) {
	cases := []struct {
		old, new Metric
	}{
		{Metric{LatencyP99Ms: -1}, Metric{}},
		{Metric{Fanout: -2}, Metric{}},
		{Metric{CostCents: -3}, Metric{}},
		{Metric{}, Metric{LatencyP99Ms: -4}},
		{Metric{}, Metric{Fanout: -5}},
		{Metric{}, Metric{CostCents: -6}},
	}
	for _, c := range cases {
		if _, err := Compare(c.old, c.new); err == nil {
			t.Fatalf("Compare(%+v, %+v) = nil error, want error", c.old, c.new)
		}
	}
}

cd .local/checks/webapp-lab && go test ./internal/feedmig/ -run 'TestCompare' -count=1 -v

=== RUN   TestCompareImproved
--- PASS: TestCompareImproved (0.00s)
=== RUN   TestCompareFanoutRegression
--- PASS: TestCompareFanoutRegression (0.00s)
=== RUN   TestCompareMixed
--- PASS: TestCompareMixed (0.00s)
=== RUN   TestCompareFlat
--- PASS: TestCompareFlat (0.00s)
=== RUN   TestCompareRejectsNegative
--- PASS: TestCompareRejectsNegative (0.00s)
PASS
ok  	webapp/internal/feedmig	0.250s