Docker DB connection refused error while attaching DB to web container

I am new to docker and trying to dockerize my laravel app (version 5.1)

Following is my docker-compose.yml

version: '3'
services:
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: test
    ports:
      - "3307:3306/tcp"
    volumes:
      - test_db:/var/lib/test_db/data
  web:
    build:
      context: ../
      dockerfile: deploy/Dockerfile
      args:
        APP_ENV: "local"
    environment:
      APP_DEBUG: "true"   
      DB_HOST: "db"
      DB_DATABASE: "test"
      DB_USERNAME: "root"
      DB_PASSWORD: "root"      
    ports:
      - "443:8000/tcp"
    volumes:
      - ../:/var/www/html
    links:
      - db
    depends_on:
      - db     
    restart: on-failure:10
    container_name: test_web 
volumes:
  test_db:  

When I execute docker-compose up command, I get the following error

[PDOException]                             
test_web |   SQLSTATE[HY000] [2002] Connection refused

As I have set 10 retries so it ultimately connects and migrations are executed but I have the following issues:

• Why the connection do not get established instantly or within few retries?
• I am using named volumes but the data dont seem to get persistent. Everytime when i run docker-compose up, migrations are executed and the data gets overwritten

Please let me know what are the possible issue behind the above two issues

via Chebli Mohamed