@Override
    public void channelRead0(ChannelHandlerContext ctx, LlapOutputSocketInitMessage msg) {
      String id = msg.getFragmentId();
      byte[] tokenBytes = msg.hasToken() ? msg.getToken().toByteArray() : null;
      try {
        registerReader(ctx, id, tokenBytes);
      } catch (Throwable t) {
        // Make sure we fail the channel if something goes wrong.
        // We internally handle all the "expected" exceptions, so log a lot of information here.
        failChannel(ctx, id, StringUtils.stringifyException(t));
      }
    }
Responsible for sending back result set data to the connections
made by external clients via the LLAP input format.
ql/src/java/org/apache/hadoop/hive/llap/LlapOutputFormatService.java