Add metric for FindMissing digest count. (#9151)

Author: vadimberezniker

enterprise/server/backends/pebble_cache/pebble_cache.go

@@ -1582,6 +1582,8 @@ func (p *PebbleCache) FindMissing(ctx context.Context, resources []*rspb.Resourc
 	}
 	defer db.Close()
 
+	metrics.PebbleCacheFindMissingDigestCount.With(prometheus.Labels{metrics.CacheNameLabel: p.name}).Add(float64(len(resources)))
+
 	var missing []*repb.Digest
 	for _, r := range resources {
 		err = p.findMissing(ctx, db, r)

server/metrics/metrics.go

@@ -3056,6 +3056,15 @@ var (
 		CacheNameLabel,
 	})
 
+	PebbleCacheFindMissingDigestCount = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: bbNamespace,
+		Subsystem: "remote_cache",
+		Name:      "pebble_cache_find_missing_digest_count",
+		Help:      "Count of digests within FindMissing requests.",
+	}, []string{
+		CacheNameLabel,
+	})
+
 	// ## Podman metrics
 
 	PodmanSociStoreCrashes = promauto.NewCounter(prometheus.CounterOpts{