diff --git a/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterShardingSettings.scala b/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterShardingSettings.scala
index 3921dc7a52..a9f92b0c1d 100644
--- a/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterShardingSettings.scala
+++ b/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/ClusterShardingSettings.scala
@@ -23,6 +23,7 @@ object ClusterShardingSettings {
   val StateStoreModeDData = "ddata"
 
   /**
+   * Only for testing
    * INTERNAL API
    */
   @InternalApi
diff --git a/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/Shard.scala b/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/Shard.scala
index 864365328c..c7a6066a44 100644
--- a/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/Shard.scala
+++ b/akka-cluster-sharding/src/main/scala/akka/cluster/sharding/Shard.scala
@@ -247,6 +247,7 @@ private[akka] object Shard {
     private val entities: java.util.Map[EntityId, EntityState] = new util.HashMap[EntityId, EntityState]()
     // needed to look up entity by reg when a Passivating is received
     private val byRef = new util.HashMap[ActorRef, EntityId]()
+    // optimization to not have to go through all entities to find batched writes
     private val remembering = new util.HashSet[EntityId]()
 
     def alreadyRemembered(set: Set[EntityId]): Unit = {