Merge pull request #36889 from wojtek-t/reuse_fields_and_labels

Automatic merge from submit-queue

Reuse fields and labels

This should significantly reduce memory allocations in apiserver in large cluster.
Explanation:
- every kubelet is refreshing watch every 5-10 minutes (this generally is not causing relist - it just renews watch)
- that means, in 5000-node cluster, we are issuing ~10 watches per second
- since we don't have "watch heartbets", the watch is issued from previously received resourceVersion
- to make some assumption, let's assume pods are evenly spread across pods, and writes for them are evenly spread - that means, that a given kubelet is interested in 1 per 5000 pod changes
- with that assumption, each watch, has to process 2500 (on average) previous watch events
- for each of such even, we are currently computing fields.

This PR is fixing this problem.

examples/apiserver/rest/reststorage.go

@@ -40,8 +40,15 @@ func NewREST(config *storagebackend.Config, storageDecorator generic.StorageDeco
 	newListFunc := func() runtime.Object { return &testgroup.TestTypeList{} }
 	// Usually you should reuse your RESTCreateStrategy.
 	strategy := &NotNamespaceScoped{}
+	getAttrs := func(obj runtime.Object) (labels.Set, fields.Set, error) {
+		testObj, ok := obj.(*testgroup.TestType)
+		if !ok {
+			return nil, nil, fmt.Errorf("not a TestType")
+		}
+		return labels.Set(testObj.Labels), nil, nil
+	}
 	storageInterface, _ := storageDecorator(
-		config, 100, &testgroup.TestType{}, prefix, strategy, newListFunc, storage.NoTriggerPublisher)
+		config, 100, &testgroup.TestType{}, prefix, strategy, newListFunc, getAttrs, storage.NoTriggerPublisher)
 	store := &registry.Store{
 		NewFunc: func() runtime.Object { return &testgroup.TestType{} },
 		// NewListFunc returns an object capable of storing results of an etcd list.