Enable progress notify events in watchcache

staging/src/k8s.io/apiserver/pkg/features/kube_features.go

@@ -138,6 +138,12 @@ const (
 	//
 	// Allows sending warning headers in API responses.
 	WarningHeaders featuregate.Feature = "WarningHeaders"
+
+	// owner: @wojtek-t
+	// alpha: v1.20
+	//
+	// Allows for updating watchcache resource version with progress notify events.
+	EfficientWatchResumption featuregate.Feature = "EfficientWatchResumption"
 )
 
 func init() {
@@ -162,4 +168,5 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 	RemoveSelfLink:           {Default: true, PreRelease: featuregate.Beta},
 	SelectorIndex:            {Default: true, PreRelease: featuregate.Beta},
 	WarningHeaders:           {Default: true, PreRelease: featuregate.Beta},
+	EfficientWatchResumption: {Default: false, PreRelease: featuregate.Alpha},
 }

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go

@@ -1098,7 +1098,14 @@ func (lw *cacherListerWatcher) List(options metav1.ListOptions) (runtime.Object,
 
 // Implements cache.ListerWatcher interface.
 func (lw *cacherListerWatcher) Watch(options metav1.ListOptions) (watch.Interface, error) {
-	return lw.storage.WatchList(context.TODO(), lw.resourcePrefix, storage.ListOptions{ResourceVersion: options.ResourceVersion, Predicate: storage.Everything})
+	opts := storage.ListOptions{
+		ResourceVersion: options.ResourceVersion,
+		Predicate:       storage.Everything,
+	}
+	if utilfeature.DefaultFeatureGate.Enabled(features.EfficientWatchResumption) {
+		opts.ProgressNotify = true
+	}
+	return lw.storage.WatchList(context.TODO(), lw.resourcePrefix, opts)
 }
 
 // errWatcher implements watch.Interface to return a single error

staging/src/k8s.io/apiserver/pkg/storage/cacher/watch_cache.go

@@ -381,6 +381,29 @@ func (w *watchCache) doCacheResizeLocked(capacity int) {
 	w.capacity = capacity
 }
 
+func (w *watchCache) UpdateResourceVersion(resourceVersion string) {
+	rv, err := w.versioner.ParseResourceVersion(resourceVersion)
+	if err != nil {
+		klog.Errorf("Couldn't parse resourceVersion: %v", err)
+		return
+	}
+
+	w.Lock()
+	defer w.Unlock()
+	w.resourceVersion = rv
+
+	// Don't dispatch bookmarks coming from the storage layer.
+	// They can be very frequent (even to the level of subseconds)
+	// to allow efficient watch resumption on kube-apiserver restarts,
+	// and propagating them down may overload the whole system.
+	//
+	// TODO: If at some point we decide the performance and scalability
+	// footprint is acceptable, this is the place to hook them in.
+	// However, we then need to check if this was called as a result
+	// of a bookmark event or regular Add/Update/Delete operation by
+	// checking if resourceVersion here has changed.
+}
+
 // List returns list of pointers to <storeElement> objects.
 func (w *watchCache) List() []interface{} {
 	return w.store.List()