yii2.0主从数据库实现源码分析-----（二）

来源：互联网发布：mac顶部菜单栏编辑：程序博客网时间：2024/06/05 22:32

这篇主要是介绍当主或者从服务器挂掉之后，yii的处理

connection.php

        $cache = is_string($this->serverStatusCache) ? Yii::$app->get($this->serverStatusCache, false) : $this->serverStatusCache;<span style="color:#ff0000;">//获取配置文件中的cache</span>        shuffle($pool);        foreach ($pool as $config) {<span style="color:#ff0000;">//遍历数据库配置项，从这里也看出来了，再配置数据库的时候，一般masters/slaves是个二维数组，而config是一维的用来共享</span>            $config = array_merge($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)) {<span style="color:#ff0000;">//会先判断cache里面是否有$key，有$key说明这个库连接失败过，而且还没过那个时间</span>                // 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, $this->serverRetryInterval);<span style="color:#ff0000;">//初始化PDO失败，写入缓存记录，有效期是$this->serverRetryInterval</span>                }            }        }

接着看下connection.php里面的一些属性

    /**     * @var Cache|string the cache object or the ID of the cache application component that is used to store     * the health status of the DB servers specified in [[masters]] and [[slaves]].     * This is used only when read/write splitting is enabled or [[masters]] is not empty.     */    public $serverStatusCache = 'cache';<span style="color:#ff0000;">//缓存，存放标志位</span>    /**     * @var integer the retry interval in seconds for dead servers listed in [[masters]] and [[slaves]].     * This is used together with [[serverStatusCache]].     */    public $serverRetryInterval = 600;<span style="color:#ff0000;">//时间，过多久之后才会重试之前宕掉的数据库服务器</span>

在main.php中

<?phpreturn [    'vendorPath' => dirname(dirname(__DIR__)) . '/vendor',    'components' => [        'cache' => [            'class' => 'yii\caching\FileCache',<span style="color:#ff0000;">//默认的缓存配置</span>        ],    ],];

从上面的源码中可以看出来，每次请求到来，yii初始化PDO的时候，对于上次宕掉的数据库服务器，采用了标志位避免了轮询，而是每隔一定的时间，来初始化

清除缓存的方法

$cache=Yii::$app->get("cache");$cache->flush();

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