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 dfa91515cca6432f38b102d2a119ca230e3655b5..b614920f84494f8cee4bea389b55049d25576fb9 100644
--- a/service/datastore/properties.go
+++ b/service/datastore/properties.go
@@ -414,7 +414,7 @@ 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] != '$' {
+		if withMeta || !isMetaKey(k) {
 			ret[k] = append(ret[k], v...)
 		}
 	}
@@ -450,3 +450,21 @@ func (pm PropertyMap) SetMeta(key string, val interface{}) error {
 func (pm PropertyMap) Problem() error {
 	return nil
 }
+
+// DataLen returns the number of non-metadata rows in this PropertyMap.
+func (pm PropertyMap) DataLen() int {
+	ret := 0
+	for k := range pm {
+		if isMetaKey(k) {
+			continue
+		}
+		ret++
+	}
+	return ret
+}
+
+func isMetaKey(k string) bool {
+	// empty counts as a metakey since it's not a valid data key, but it's
+	// not really a valid metakey either.
+	return k == "" || k[0] == '$'
+}