code: public static Message buildSyncHistory(Zxid lastZxid) {
      ZabMessage.Zxid zxid = toProtoZxid(lastZxid);
      ZabMessage.SyncHistory sync =
        ZabMessage.SyncHistory.newBuilder().setLastZxid(zxid).build();
      return Message.newBuilder().setType(MessageType.SYNC_HISTORY)
                                 .setSyncHistory(sync).build();
    }
docs: Creates a SYNC_HISTORY message. Leader will synchronize everything it has
  to follower after receiving this message.