// server.js
var process = require('child_process');
var fs = require('fs');
var db_rwp = process.fork('db_rwp.js');
    db_rwp.on('message', function(data) {
      switch(data.acid){
        /* INIT : ERROR  */ case 'error':
            console.log(' # database reader / writer ERROR  ');
            console.log(data.arg1);
          break;
        /* INIT :  OK!   */ case 'success':
            console.log(' # database reader / writer : 0N   ');
          break;
        }
    });

// db_rwp.js
var mysql = require('mysql');
var fs = require('fs');
//When Spawned Return Connection Status
var db = mysql.createConnection({
    host:'host', user:'user', password:'pass', database: 'database'
});
db.connect(function(err){
    if (err) { process.send({acid:'error',arg1:err}); }
    else { process.send({acid:'success'});}
});

// server.js -to- db_rwp.js :
db_rwp.send({acid:'action_id', csid:socket.id});
// db_rwp.js -to- server.js :
process.send({acid:'action_id', csid:data.csid});