Request TTFB metric for GetObject API

pkg/api/controller.go

@@ -4480,6 +4480,7 @@ func (c *Controller) GetObject(w http.ResponseWriter, r *http.Request, repositor
 	}
 	ctx := r.Context()
 	c.LogAction(ctx, "get_object", r, repository, ref, "")
+	requestStart := time.Now()
 
 	repo, err := c.Catalog.GetRepository(ctx, repository)
 	if c.handleAPIError(ctx, w, r, err) {
@@ -4564,6 +4565,11 @@ func (c *Controller) GetObject(w http.ResponseWriter, r *http.Request, repositor
 		w.Header().Set("Content-Length", fmt.Sprint(entry.Size))
 	}
 
+	// time to first byte - include out part of the processing without the actual data transfer
+	requestTTFBHistograms.
+		WithLabelValues("GetObject").
+		Observe(time.Since(requestStart).Seconds())
+
 	// copy the content
 	_, err = io.Copy(w, reader)
 	if err != nil {

pkg/api/stats.go

@@ -20,3 +20,11 @@ var requestHistograms = promauto.NewHistogramVec(
 		Buckets: []float64{0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60},
 	},
 	[]string{"operation", "code"})
+
+var requestTTFBHistograms = promauto.NewHistogramVec(
+	prometheus.HistogramOpts{
+		Name:    "api_request_ttfb_duration_seconds",
+		Help:    "request time-to-first-byte durations for lakeFS API",
+		Buckets: []float64{0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 30, 60},
+	},
+	[]string{"operation"})