Federico Cargnelutti

Packt Publishing recently sent me a copy of the book “Symfony 1.3 Web Application Development” to review.

This book is not a reference guide, but an example driven tutorial that takes you through the process of building Model-View-Controller-based web applications. You will learn how to create and develop a simple online store application. It also covers best practices for better and quicker application development.

The book is based on the latest version of the Symfony Framework, and does a great job telling you what you get out of the box and how it works, which is perfect for hitting the ground running. During the development you are introduced to the concepts and features of the MVC framework. However, for those who want to know more about the framework, the book doesn’t explain how things work under the covers. This book is more for beginners who want to get started with Symfony 1.3.

One thing I didn’t like about this book is that it uses Propel instead of Doctrine as the default ORM framework. Apart from that, it does a great job explaining and demonstrating with practical examples how to build a Web application from scratch.

Overall, and considering that some of the topics in this book have already been covered in Practical Symfony 1.3, I rate this book 4 out of 5.

Symfony 1.3 Web Application Development

Last updated: 21 Feb, 2010

Database replication is an option that allows the content of one database to be replicated to another database or databases, providing a mechanism to scale out the database. Scaling out the database allows more activities to be processed and more users to access the database by running multiple copies of the databases on different machines.

The problem with monolithic database designs is that they don’t establish an infrastructure that allows for rapid changes in business requirements. Here is where database replication comes into play. Replication can be used effectively for many different purposes, such as separating data entry and reporting, distributing load across servers, providing high availability, etc.

Zf_Orm_DataSource is a Zend Framework Replication Adapter class flexible enough to support the most commonly used replication scenarios:

Single-Master Replication

In the simplest replication scenario, the master copy of directory data is held in a single read-write replica on one server called the supplier server. The supplier server also maintains changelog for this replica. On another server, called the consumer server, there can be multiple read-only replicas.

Configuration array:

$config = array(
    'adapter'        => 'Pdo_Mysql',
    'driver_options' => array(PDO::ATTR_TIMEOUT=>5),
    'username'       => 'root',
    'password'       => 'root',
    'dbname'         => 'test',
    'master_servers' => 1,
    'servers'        => array(
        array('host' => 'db.master-1.com'),
        array('host' => 'db.slave-1.com'),
        array('host' => 'db.slave-2.com')
    )
);

// or ...

$config = array(
    'adapter'        => 'Pdo_Mysql',
    'driver_options' => array(PDO::ATTR_TIMEOUT=>5),
    'dbname'         => 'test',
    'master_servers' => 1,
    'servers'        => array(
        array('host' => 'db.master-1.com', 'username' => 'user1', 'password'=>'pass1'),
        array('host' => 'db.slave-1.com', 'username' => 'user2', 'password' => 'pass2'),
        array('host' => 'db.slave-2.com', 'username' => 'user3', 'password' => 'pass3')
    )
);

In the setup above, all writes will go to the master connection and all reads will be randomly distributed across the available slaves.

Multi-Master Replication

This type of configuration can work with any number of consumer servers. Each consumer server holds a read-only replica. The consumers can receive updates from all the suppliers. The consumers also have referrals defined for all the suppliers to forward any update requests that the consumers receive.

$config = array(
    'adapter'        => 'Pdo_Mysql',
    'driver_options' => array(PDO::ATTR_TIMEOUT=>5),
    'username'       => 'root',
    'password'       => 'root',
    'dbname'         => 'test',
    'master_servers' => 2,
    'master_read'    => true,
    'servers'        => array(
        array('host' => 'db.master-1.com'),
        array('host' => 'db.master-2.com')
    )
);

Using a distributed memory caching system

Database connections are expensive and it’s very inefficient for an application to try to connect to a server that is down or not responding. A distributed memory caching system can help alleviate this problem by keeping a list of all the failed connections in memory, sharing that information across multiple servers and allowing the application to access it before attempting to open a connection.

To enable this option, you have to pass an instance of the Memcached adapter class:

class Bootstrap extends Zend_Application_Bootstrap_Base
{
    protected function _initCache()
    {
        ...
    }

    protected function _initDatabase()
    {
        $config = include APPLICATION_PATH . '/config/database.php';
        $cache = $this->getResource('cache');
        $dataSource = new Zf_Orm_DataSource($config, $cache, 'cache_tag');
        Zend_Registry::set('dataSource', $dataSource);
    }
}

And here is a short example of how the Replication Adapter might be used in a ZF application:

class TestDao
{
    public function fetchAll()
    {
        $db = Zend_Registry::get('dataSource')->getConnection('slave');
        $query = $db->select()->from('test');
        return $db->fetchAll($query);
    }

    public function insert($data)
    {
        $db = Zend_Registry::get('dataSource')->getConnection('master');
        $db->insert('test', $data);
        return $db->lastInsertId();
    }
}

Source Code:
http://fedecarg.com/repositories/show/replicationadapter