yii2数据库配置一主多从和多主多从

yii2配置文件如下：

[
 'class' => 'yii\db\Connection',

 // common configuration for masters
 'masterConfig' => [
 'username' => 'master',
 'password' => '',
 'attributes' => [
 // use a smaller connection timeout
 PDO::ATTR_TIMEOUT => 10,
 ],
 ],

 // list of master configurations
 'masters' => [
 ['dsn' => 'dsn for master server 1'],
 ['dsn' => 'dsn for master server 2'],
 ],

 // common configuration for slaves
 'slaveConfig' => [
 'username' => 'slave',
 'password' => '',
 'attributes' => [
 // use a smaller connection timeout
 PDO::ATTR_TIMEOUT => 10,
 ],
 ],

 // list of slave configurations
 'slaves' => [
 ['dsn' => 'dsn for slave server 1'],
 ['dsn' => 'dsn for slave server 2'],
 ['dsn' => 'dsn for slave server 3'],
 ['dsn' => 'dsn for slave server 4'],
 ],
]

protected function openFromPool(array $pool, array $sharedConfig)
{
if (empty($pool)) {
return null;
}

if (!isset($sharedConfig[‘class’])) {
$sharedConfig[‘class’] = get_class($this);
}

$cache = is_string($this->serverStatusCache) ? Yii::$app->get($this->serverStatusCache, false) : $this->serverStatusCache;

shuffle($pool);//源码这里随机读取配置

foreach ($pool as $config) {
$config = array_merge($sharedConfig, $config);
if (empty($config[‘dsn’])) {
throw new InvalidConfigException(‘The “dsn” option must be specified.’);
}

$key = [__METHOD__, $config[‘dsn’]];
if ($cache instanceof Cache && $cache->get($key)) {
// should not try this dead server now
continue;
}

/* @var $db Connection */
$db = Yii::createObject($config);

try {
$db->open();
return $db;
} catch (\Exception $e) {
Yii::warning(“Connection ({$config[‘dsn’]}) failed: ” . $e->getMessage(), __METHOD__);
if ($cache instanceof Cache) {
// mark this server as dead and only retry it after the specified interval
$cache->set($key, 1, $this->serverRetryInterval);
}
}
}

return null;
}