Refactor keys and queries in datastore service and implementation.

filter/dscache/context.go

Index: filter/dscache/context.go
diff --git a/filter/dscache/context.go b/filter/dscache/context.go
index 0233b486af9ee8dd0c03841a7d38e2cd73e35d1c..a9f10ba1de6fbf0955edf5800ce4f3842925c0e6 100644
--- a/filter/dscache/context.go
+++ b/filter/dscache/context.go
@@ -28,7 +28,7 @@ var dsTxnCacheKey key
 // setting.
 //
 // If shardsForKey is nil, the value of DefaultShards is used for all keys.
-func FilterRDS(c context.Context, shardsForKey func(ds.Key) int) context.Context {
+func FilterRDS(c context.Context, shardsForKey func(*ds.Key) int) context.Context {
 	if !IsGloballyEnabled(c) {
 		return c
 	}