关于GatewayWorker中Db单例的疑问

根据GatewayWorker文档中的描述：
DB属于单例模式，在onXXX里初始化的数据库单例只属于当前子进程自己所有；
那么我是不是可以如下理解：

<?php
$worker = new BusinessWorker();
$worker->name = 'YourAppBusinessWorker';
$worker->count = 4;
$worker->registerAddress = '127.0.0.1:1238';
$worker->onWorkerStart = function()
{
    Db::instance('db1');
};
$worker->onMessage = function()
{
    $ret = Db->select('name,age')->from('users')->where('age>12')->query();
}
if(!defined('GLOBAL_START'))
{
    Worker::runAll();
}

那么这样做的话，我就有一个问题了，如果这里我需要进行2个数据库实例怎么办？下面这么做我感觉是不正确的：

<?php
$worker = new BusinessWorker();
$worker->name = 'YourAppBusinessWorker';
$worker->count = 4;
$worker->registerAddress = '127.0.0.1:1238';
$db1 = null;
$db2 = null;
$worker->onWorkerStart = function()
{
    $db1 = Db::instance('db1');
    $db2 = Db::instance('db2');
};
$worker->onMessage = function()
{
    $ret1 = $db1->select('name,age')->from('users')->where('age>12')->query();
    $ret2 = $db2->select('name,age')->from('users')->where('age>12')->query();
}
if(!defined('GLOBAL_START'))
{
    Worker::runAll();
}