public synchronized Set<MessageInfo> getReceivedStoreMessagesWithUpdatesPending() {
      return receivedStoreMessagesWithUpdatesPending == null ? Collections.emptySet()
          : new HashSet<>(receivedStoreMessagesWithUpdatesPending);
    }
Get remote messages that were previously missing and are now received but whose blob properties (
ttl_update, delete, undelete) still needs to be compared to properties of blob in local store and reconciled.
@return set of messages that are now found in store as a new collection
ambry-replication/src/main/java/com/github/ambry/replication/ReplicaThread.java