feat(metrics): add cache, process and http metrics

modules/cache/cache.go

@@ -9,11 +9,33 @@ import (
 	"time"
 
 	"code.gitea.io/gitea/modules/setting"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
 
 	_ "gitea.com/go-chi/cache/memcache" //nolint:depguard // memcache plugin for cache, it is required for config "ADAPTER=memcache"
 )
 
 var defaultCache StringCache
+var hitCounter = promauto.NewCounter(prometheus.CounterOpts{
+	Namespace: "gitea",
+	Help:      "Cache hit count",
+	Subsystem: "cache",
+	Name:      "hit",
+})
+var missCounter = promauto.NewCounter(prometheus.CounterOpts{
+	Namespace: "gitea",
+	Help:      "Cache miss count",
+	Subsystem: "cache",
+	Name:      "miss",
+})
+var latencyHistogram = promauto.NewHistogram(
+	prometheus.HistogramOpts{
+		Namespace: "gitea",
+		Help:      "Cache latency",
+		Subsystem: "cache",
+		Name:      "duration",
+	},
+)
 
 // Init start cache service
 func Init() error {

modules/cache/string_cache.go

@@ -6,6 +6,7 @@ package cache
 import (
 	"errors"
 	"strings"
+	"time"
 
 	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/setting"
@@ -63,10 +64,15 @@ func (sc *stringCache) Ping() error {
 }
 
 func (sc *stringCache) Get(key string) (string, bool) {
+	start := time.Now()
 	v := sc.chiCache.Get(key)
+	elapsed := time.Since(start).Seconds()
+	latencyHistogram.Observe(elapsed)
 	if v == nil {
+		missCounter.Add(1)
 		return "", false
 	}
+	hitCounter.Add(1)
 	s, ok := v.(string)
 	return s, ok
 }