vmalert parsing json benchmark

gistfile1.txt

func BenchmarkParsePrometheusResponse(b *testing.B) {
	data, err := os.ReadFile("testdata/instant_response.json")
	if err != nil {
		b.Fatalf("error while reading file: %s", err)
	}

	runWithMem := func(name string, f func(b *testing.B)) {
		var m1, m2 runtime.MemStats
		runtime.GC()
		runtime.ReadMemStats(&m1)
		b.Run(name, f)
		runtime.ReadMemStats(&m2)
		fmt.Println("MBs allocated at heap:", float64(m2.HeapAlloc-m1.HeapAlloc)/1e6)
		fmt.Println("mallocs:", m2.Mallocs-m1.Mallocs)
	}

	debug.SetGCPercent(-1)

	// Parse with std lib and fastsjson for each `metric` object
	runWithMem("Instant std+fastjson", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			var pi promInstant
			err = pi.UnmarshalMixed(data)
			if err != nil {
				b.Fatalf("unexpected parse err: %s", err)
			}
		}
	})

	// Parse with fastjson only
	runWithMem("Instant fastjson", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			var pi promInstant
			err = pi.UnmarshalFastJson(data)
			if err != nil {
				b.Fatalf("unexpected parse err: %s", err)
			}
		}
	})

	// Old parsing before https://github.com/VictoriaMetrics/VictoriaMetrics/pull/6272
	runWithMem("Instant std", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			var pi promInstantStd
			err = json.Unmarshal(data, &pi.Result)
			if err != nil {
				b.Fatalf("unexpected parse err: %s", err)
			}
			_, err = pi.metrics()
			if err != nil {
				b.Fatalf("unexpected parse err: %s", err)
			}
		}
	})
}