Solving a 2006 MySQL error connection timeout in Magento1

In my recent task I was testing a web crawler script which uses Magento database information for the crawling requests. I have encountered the following error:

Fatal error: Uncaught exception ‘PDOException’ with message ‘SQLSTATE[HY000]: General error: 2006 MySQL server has gone away’ in lib/Zend/Db/Statement/Pdo.php:228

The Problem

This error occured after around 45 minutes of script runtime.
The script was written in a way that it was possible that there is no database interaction for a longer period.
In consequence to that when the script reached a point where it was trying to save or fetch something from the database, the mysql connection ran into a timeout – unnoticed by the script.
Thus resulting in the above mentioned MySQL error.

mysql wait_timeout

The variable controlling this timeout from MySQL is the wait_timeout system variable.

Definition from MySQL Reference Manual :

“The number of seconds the server waits for activity on a non-interactive connection before closing it.”

As it turns out we have already had this situation in another project – thanks to the netz98 developers for the hint.

The Solution

The solution is to close the connection before using it – in case of long running and un-interrupted code part that does no database communication.

We have added the following code snippet to our ResourceModel:

/**
 * Initialize the ReadAdapter (force a re-connect)
 *
 * @param bool $useNewConnection
 * @return Varien_Db_Adapter_Pdo_Mysql
 */
protected function _initReadAdapter($useNewConnection = false)
{
    /** @var Varien_Db_Adapter_Pdo_Mysql $adapter */
    $adapter = $this->_getReadAdapter();

    /**
     * In some occasions we want to use a fresh connection to fetch table data
     * when crawling takes longer (between queries) than the configured mysql wait_timeout
     *
     */
    if ($useNewConnection === true) {
        $adapter->closeConnection();
    }
    return $adapter;
}

With this method the Connection within the Adapter can be closed. When it is closed the connection will be re-initialized automatically with the next Database Interaction that is triggered by our code. To do so we introduced the parameter $useNewConncetion which enforces this behaviour.

Each time we have reached a point in our script where it could be possible that the connection hit the wait_timeout we just call this method with useNewConnection set to true.

I hope this article is helpful for you, in case you face the same situation. Feel free to comment if you faced this issue too or if you have any additions.

Update: Keep alive implementation by Ivan Chepurnyi (@IvanChepurnyi)

    /**
     * Zend db adapter validation, in order to get rid of possible server gone away
     *
     * @param Zend_Db_Adapter_Abstract $adapter
     * @return bool
     */
    protected function _validateConnection(Zend_Db_Adapter_Abstract $adapter)
    {
        try {
            // Execute simple non heavy query
            return $adapter->fetchOne('SELECT 1') === '1';
        } catch (Zend_Db_Statement_Exception $e) {
            $adapter->closeConnection();
        }

        return $adapter->getConnection() !== null;
    }