feat: add mem_sys_bytes metrics

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## 1.0.0-dev
 
+- Add `mem_sys_bytes` metric. ([@palkan][])
+
+Returns the total bytes of memory obtained from the OS
+(according to [`runtime.MemStats.Sys`](https://golang.org/pkg/runtime/#MemStats)).
+
 - Add `--enable_ws_compression` option to enable WebSocket per message compression. ([@palkan][])
 
 Disabled by default due to the experimental status in [Gorilla](https://github.com/gorilla/websocket/blob/c3e18be99d19e6b3e8f1559eea2c161a665c4b6b/doc.go#L201-L214).

metrics/gauge.go

@@ -31,6 +31,11 @@ func (g *Gauge) Set(value int) {
 	atomic.StoreInt64(&g.value, int64(value))
 }
 
+// Set64 sets gauge value as int64
+func (g *Gauge) Set64(value int64) {
+	atomic.StoreInt64(&g.value, value)
+}
+
 // Value returns the current gauge value
 func (g *Gauge) Value() int64 {
 	return atomic.LoadInt64(&g.value)

node/node.go

@@ -18,6 +18,7 @@ const (
 	statsCollectInterval = 5 * time.Second
 
 	metricsGoroutines      = "goroutines_num"
+	metricsMemSys          = "mem_sys_bytes"
 	metricsClientsNum      = "clients_num"
 	metricsUniqClientsNum  = "clients_uniq_num"
 	metricsStreamsNum      = "broadcast_streams_num"
@@ -341,6 +342,10 @@ func (n *Node) collectStats() {
 func (n *Node) collectStatsOnce() {
 	n.Metrics.Gauge(metricsGoroutines).Set(runtime.NumGoroutine())
 
+	var m runtime.MemStats
+	runtime.ReadMemStats(&m)
+	n.Metrics.Gauge(metricsMemSys).Set64(int64(m.Sys))
+
 	n.Metrics.Gauge(metricsClientsNum).Set(n.hub.Size())
 	n.Metrics.Gauge(metricsUniqClientsNum).Set(n.hub.UniqSize())
 	n.Metrics.Gauge(metricsStreamsNum).Set(n.hub.StreamsSize())
@@ -349,6 +354,7 @@ func (n *Node) collectStatsOnce() {
 
 func (n *Node) registerMetrics() {
 	n.Metrics.RegisterGauge(metricsGoroutines, "The number of Go routines")
+	n.Metrics.RegisterGauge(metricsMemSys, "The total bytes of memory obtained from the OS")
 
 	n.Metrics.RegisterGauge(metricsClientsNum, "The number of active clients")
 	n.Metrics.RegisterGauge(metricsUniqClientsNum, "The number of unique clients (with respect to connection identifiers)")