流回HTTP响应的最佳方法？

Question

I have a REST service which may have to return more than 1000,000 rows from the database. I am doing it by opening an output stream. Basically I am getting printwriter from HTTP-RESPONSE and streaming it back as I get it from database rather than storing all in the memory and then returning back.

sth like this:-

 @Override
      public void processRow(ResultSet resultSet) throws SQLException {
         String data = resultSet.getString("data");
            printWriter.write(data);
            printWriter.flush();
         }
      }

My question is do we get any performance gain by flushing in a bucket? Something like storing 5000 rows in a stringbuffer and then flushing it out rather than flushing it per row.

Answer 1

Each flush will make system to 'flush' data through all buffers down to network layer or, it depends on libraries you are using, might even block till remote side will acknowledge that data has arrived. That means that it will be a lots of time spent in I/O blocking aka 'it will be really slow'.

I would recommend to remove flush here, make a BufferedOutputStream with reasonably small (512-8192 bytes) and create PrintWriter over it and perform measurements with different buffer sizes.