gistfile1.php

<?php

// config/ProjectConfiguration.class.php
class ProjectConfiguration extends sfProjectConfiguration
{
  protected
    $masterConnection = null,
    $slaveConnection  = null;

  public function initializeConnections()
  {
    $slaves = array();
    foreach (Doctrine_Manager::getInstance()->getConnections() as $name => $conn)
    {
      switch (true)
      {
        case 'master' == $name:
          $this->masterConnection = $conn;
          break;
        case 0 === strpos($name, 'slave'):
          $slaves[] = $conn;
          break;
      }
    }

    if (is_null($this->masterConnection))
    {
      $this->masterConnection = Doctrine_Manager::connection();
    }

    // choose one slave connection for the current request
    $this->slaveConnection = count($slaves) ?
      $slaves[rand(0, count($slaves) - 1)] :
      Doctrine_Manager::connection();
  }

  public function getMasterConnection()
  {
    $this->masterConnection || $this->initializeConnections();
    return $this->masterConnection;
  }

  public function getSlaveConnection()
  {
    $this->slaveConnection || $this->initializeConnections();
    return $this->slaveConnection;
  }
}