hello.go

package main

import (
  "database/sql"
	"encoding/json"
	"html/template"
	"log"
	"math/rand"
	"net/http"
	"runtime"

	_ "github.com/go-sql-driver/mysql"
)

type Message struct {
	Message string `json:"message"`
}

type World struct {
	Id           uint16 `json:"id"`
	RandomNumber uint16 `json:"randomNumber"`
}

type Fortune struct {
	Id      uint16 `json:"id"`
	Message string `json:"message"`
}

// TODO: remove ?charset=utf8 from DSN after the next Go-MySQL-Driver release
// https://github.com/go-sql-driver/mysql#unicode-support
const (
	// Database
	connectionString   = "root:@tcp(localhost:3306)/hello_world?charset=utf8"
	worldSelect        = "SELECT id, randomNumber FROM World WHERE id = ?"
	fortuneSelect      = "SELECT id, message FROM Fortune;"
	//worldRowCount      = 10000
	worldRowCount      = 6
	maxConnectionCount = 256

	helloWorldString = "Hello, World!"
)

var (
	// Templates
	tmpl = template.Must(template.ParseFiles("templates/layout.html", "templates/fortune.html"))

	// Database
	worldStatement   *sql.Stmt
	updateStatement  *sql.Stmt

	helloWorldBytes = []byte(helloWorldString)
)

func main() {
	runtime.GOMAXPROCS(runtime.NumCPU())

	db, err := sql.Open("mysql", connectionString)
	if err != nil {
		log.Fatalf("Error opening database: %v", err)
	}
	db.SetMaxIdleConns(maxConnectionCount)
	worldStatement, err = db.Prepare(worldSelect)
	if err != nil {
		log.Fatal(err)
	}

	http.HandleFunc("/", dbHandler)
	http.ListenAndServe(":8080", nil)
}

// Test 2: Single database query
func dbHandler(w http.ResponseWriter, r *http.Request) {
	var world World
	err := worldStatement.QueryRow(rand.Intn(worldRowCount)+1).Scan(&world.Id, &world.RandomNumber)
	if err != nil {
		log.Fatalf("Error scanning world row: %s", err.Error())
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(&world)
}

type Fortunes []*Fortune

func (s Fortunes) Len() int      { return len(s) }
func (s Fortunes) Swap(i, j int) { s[i], s[j] = s[j], s[i] }

type ByMessage struct{ Fortunes }

func (s ByMessage) Less(i, j int) bool { return s.Fortunes[i].Message < s.Fortunes[j].Message }

hello.rb

require 'json'
require 'eventmachine'
require 'mysql2/em'
require './pool'
$MAX_RECORD = 6

class Server < EventMachine::Connection

  def receive_data(data)
    $client.query "SELECT * from World where id = #{rand(6) + 1}" do |result|
      send_data JSON.dump(result.to_a)
      close_connection_after_writing
    end
  end
end

EM.run do
  EM.next_tick do
    $client = Pool.new username: "root", database: "hello_world", size: 20
  end

  EM.start_server '0.0.0.0', 3001, Server
end

pool.rb

require 'json'
require 'eventmachine'
require 'mysql2/em'
require './pool'
$MAX_RECORD = 6

class Server < EventMachine::Connection

  def receive_data(data)
    $client.query "SELECT * from World where id = #{rand(6) + 1}" do |result|
      send_data JSON.dump(result.to_a)
      close_connection_after_writing
    en
  end
end

EM.run do
  EM.next_tick do
    $client = Pool.new username: "root", database: "hello_world", size: 20
  end

  EM.start_server '0.0.0.0', 3001, Server
end