Optimize selector for single-matching items

Kubernetes-commit: f93a270edcefc3780247ae89eea02cd13b81237b

pkg/registry/generic/registry/store.go

@@ -1036,7 +1036,16 @@ func (e *Store) Watch(ctx genericapirequest.Context, options *metainternalversio
 func (e *Store) WatchPredicate(ctx genericapirequest.Context, p storage.SelectionPredicate, resourceVersion string) (watch.Interface, error) {
 	if name, ok := p.MatchesSingle(); ok {
 		if key, err := e.KeyFunc(ctx, name); err == nil {
-			w, err := e.Storage.Watch(ctx, key, resourceVersion, p)
+			// For performance reasons, we can optimize the further computations of
+			// selector, by removing then "matches-single" fields, because they are
+			// already satisfied by choosing appropriate key.
+			sp, err := p.RemoveMatchesSingleRequirements()
+			if err != nil {
+				glog.Warningf("Couldn't remove matches-single requirements: %v", err)
+				// Since we couldn't optimize selector, reset to the original one.
+				sp = p
+			}
+			w, err := e.Storage.Watch(ctx, key, resourceVersion, sp)
 			if err != nil {
 				return nil, err
 			}

pkg/storage/selection_predicate.go

@@ -65,16 +65,41 @@ func (s *SelectionPredicate) MatchesLabelsAndFields(l labels.Set, f fields.Set)
 	return matched
 }
 
+const matchesSingleField = "metadata.name"
+
+func removeMatchesSingleField(field, value string) (string, string, error) {
+	if field == matchesSingleField {
+		return "", "", nil
+	}
+	return field, value, nil
+}
+
 // MatchesSingle will return (name, true) if and only if s.Field matches on the object's
 // name.
 func (s *SelectionPredicate) MatchesSingle() (string, bool) {
-	// TODO: should be namespace.name
-	if name, ok := s.Field.RequiresExactMatch("metadata.name"); ok {
+	if name, ok := s.Field.RequiresExactMatch(matchesSingleField); ok {
 		return name, true
 	}
 	return "", false
 }
 
+func (s *SelectionPredicate) RemoveMatchesSingleRequirements() (SelectionPredicate, error) {
+	var fieldsSelector fields.Selector
+	if s.Field != nil {
+		var err error
+		fieldsSelector, err = s.Field.Transform(removeMatchesSingleField)
+		if err != nil {
+			return SelectionPredicate{}, err
+		}
+	}
+	return SelectionPredicate{
+		Label:       s.Label,
+		Field:       fieldsSelector,
+		GetAttrs:    s.GetAttrs,
+		IndexFields: s.IndexFields,
+	}, nil
+}
+
 // For any index defined by IndexFields, if a matcher can match only (a subset)
 // of objects that return <value> for a given index, a pair (<index name>, <value>)
 // wil be returned.