Pimcore\Db\Wrapper::closeConnectionResource PHP Method

    protected function closeConnectionResource($resource)
    {
        if ($resource) {
            try {
                $connectionId = null;
                // unfortunately mysqli doesn't throw an exception in the case the connection is lost (issues a warning)
                // and when sending a query to the broken connection (eg. when forking)
                // so we have to handle mysqli and pdo_mysql differently
                if ($resource instanceof \Zend_Db_Adapter_Mysqli) {
                    if ($resource->getConnection()) {
                        $connectionId = $resource->getConnection()->thread_id;
                    }
                } elseif ($resource instanceof \Zend_Db_Adapter_Pdo_Mysql) {
                    $connectionId = $resource->fetchOne("SELECT CONNECTION_ID()");
                }
                Logger::debug(get_class($resource) . ": closing MySQL-Server connection with ID: " . $connectionId);
                $resource->closeConnection();
            } catch (\Exception $e) {
                // this is the case when the mysql connection has gone away (eg. when forking using pcntl)
                Logger::info($e);
            }
        }
    }