Merge pull request #2528 from prometheus/beorn7/storage2

main.go: Set GOGC to 40 by default

cmd/prometheus/main.go

@@ -20,6 +20,7 @@ import (
 	_ "net/http/pprof" // Comment this line to disable pprof endpoint.
 	"os"
 	"os/signal"
+	"runtime/debug"
 	"syscall"
 	"time"
 
@@ -44,6 +45,13 @@ func main() {
 	os.Exit(Main())
 }
 
+// defaultGCPercent is the value used to to call SetGCPercent if the GOGC
+// environment variable is not set or empty. The value here is intended to hit
+// the sweet spot between memory utilization and GC effort. It is lower than the
+// usual default of 100 as a lot of the heap in Prometheus is used to cache
+// memory chunks, which have a lifetime of hours if not days or weeks.
+const defaultGCPercent = 40
+
 var (
 	configSuccess = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: "prometheus",
@@ -73,6 +81,10 @@ func Main() int {
 		return 0
 	}
 
+	if os.Getenv("GOGC") == "" {
+		debug.SetGCPercent(defaultGCPercent)
+	}
+
 	log.Infoln("Starting prometheus", version.Info())
 	log.Infoln("Build context", version.BuildContext())