class PDOConnection

SQLite-specific implementation of a PDO connection.

SQLite does not implement row locks, so when it acquires a lock, it locks the entire database. To improve performance, by default SQLite tries to defer acquiring a write lock until the first write operation of a transaction rather than when the transaction is started. Unfortunately, this seems to be incompatible with how Drupal uses transactions, and frequently leads to deadlocks.

Therefore, this class overrides \PDO to begin transactions with a BEGIN IMMEDIATE TRANSACTION statement, for which SQLite acquires the write lock immediately. This can incur some performance cost in a high concurrency environment: it adds approximately 5% to the time it takes to execute Drupal core's entire test suite on DrupalCI, and it potentially could add more in a higher concurrency environment. However, under high enough concurrency of a Drupal application, SQLite isn't the best choice anyway, and a database engine that implements row locking, such as MySQL or PostgreSQL, is more suitable.

Because of https://bugs.php.net/42766 we have to create such a transaction manually which means we must also override commit() and rollback().

Hierarchy

• class \Drupal\sqlite\Driver\Database\sqlite\PDOConnection extends \Drupal\sqlite\Driver\Database\sqlite\PDO

Expanded class hierarchy of PDOConnection

See also

https://www.drupal.org/project/drupal/issues/1120020

File

core/modules/sqlite/src/Driver/Database/sqlite/PDOConnection.php, line 30

Namespace

class PDOConnection extends \PDO {
    
    /**
     * {@inheritdoc}
     */
    public function beginTransaction() : bool {
        return $this->exec('BEGIN IMMEDIATE TRANSACTION') !== FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function commit() : bool {
        return $this->exec('COMMIT') !== FALSE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function rollBack() : bool {
        return $this->exec('ROLLBACK') !== FALSE;
    }

}

Members