A transparent cache for datastore, backed by memcache.

service/datastore/properties.go

Index: service/datastore/properties.go
diff --git a/service/datastore/properties.go b/service/datastore/properties.go
index 11f62dc2939334b7581ee453aa541365b1c518cd..8ce5970def31e1939b3f69638c85bfca264e00de 100644
--- a/service/datastore/properties.go
+++ b/service/datastore/properties.go
@@ -431,7 +431,7 @@ func (pm PropertyMap) Save(withMeta bool) (PropertyMap, error) {
 	}
 	ret := make(PropertyMap, len(pm))
 	for k, v := range pm {
-		if withMeta || len(k) == 0 || k[0] != '$' {
+		if withMeta || !isMetaKey(k) {
 			ret[k] = append(ret[k], v...)
 		}
 	}
@@ -472,6 +472,12 @@ func (pm PropertyMap) Problem() error {
 	return nil
 }
 
+func isMetaKey(k string) bool {
+	// empty counts as a metakey since it's not a valid data key, but it's
+	// not really a valid metakey either.
+	return k == "" || k[0] == '$'
+}
+
 // GetMetaDefaultImpl is the implementation of PropertyLoadSaver.GetMetaDefault.
 //
 // It takes the normal GetMeta function, the key and the default, and returns