在Drupal的数据库层应用MySQL Master/Slave

$db_url['default'] = 'mysql://username:password@localhost/databasename';
$db_url['readonly'] = 'mysql://username:password@localhost/databasename';

function db_query($query) {
  $args = func_get_args();
  array_shift($args);
  $query = db_prefix_tables($query);
  if (isset($args[0]) and is_array($args[0])) { // 'All arguments in one array' syntax
    $args = $args[0];
  }
  _db_query_callback($args, TRUE);
  $query = preg_replace_callback(DB_QUERY_REGEXP, '_db_query_callback', $query);
 
  /*
   * Integrating multiple read/write databases
   */
  if(!db_lock_master() && strpos(strtolower($query), "select") === 0 && strpos(strtolower($query), "last_insert_id") === FALSE){
    $commits   = array('alter', 'insert', 'update', 'delete', 'flush', 'lock','create');
    $is_commit = false;
    foreach($commits as $type) {
      if((strpos(strtolower($query), "$type "))){//[insert|update|create] xxxx, need a space, otherwise, some field which is like 'user_updated' will be filter as commits
        $is_commit = true;
      }
    }
 
    if($is_commit){
      db_set_active('default');
      //drupal_set_message('default');
    } else{
      db_set_active('readonly');
      //drupal_set_message('readonly');
    }
  }
  else {
    db_set_active('default');
  }
  /*
   * End read/write router
   */
 
  return _db_query($query);
}
 
function db_lock_master($lock = null) {
  static $lock_master = false;
  if (is_null($lock)) {
    return $lock_master;
  }
  else {
    $lock_master = $lock;
    return $lock_master;
  }
}