# Drupal performance and MySQL transaction isolation levels

> Check and change the MySQL transaction isolation level for Drupal to READ COMMITTED to reduce deadlocks and improve performance.

Source: https://helpcenter.ruachost.com/apps/drupal/drupal-performance-and-mysql-transaction-isolation-levels/

When running Drupal on MySQL, the **transaction isolation level** can significantly affect site performance. By default, MySQL uses the **REPEATABLE READ** isolation level, but Drupal recommends **READ COMMITTED** to avoid deadlocks and improve efficiency. On **ruachost.com**, you may see a warning message in Drupal’s **Status report** if the isolation level is not set correctly.

## Why Isolation Levels Matter

- **REPEATABLE READ** (default in MySQL) → Can cause deadlocks and slow performance in Drupal.
- **READ COMMITTED** (recommended) → Reduces deadlocks and improves concurrency.
- Correct configuration ensures smoother database operations and faster page loads.

## Determining the Current Isolation Level

1. Log in to your server via **SSH**.
2. Access MySQL with:

   ```bash
   mysql -u username -p
   ```
3. Run the command:

   ```bash
   SHOW variables WHERE variable_name LIKE "%isolation";
   ```
4. Check the output:

   - `REPEATABLE-READ` → Default, may cause issues.
   - `READ-COMMITTED` → Recommended for Drupal.

## Changing the Isolation Level

### For Shared Hosting Accounts

1. Open the `settings.php` file in your Drupal installation (`sites/default/settings.php`).
2. Locate the database connection array.
3. Add or update the line:

   ```
   'isolation_level' => 'READ COMMITTED',
   ```
4. Save the file and refresh the **Status report** page in Drupal.
5. The warning message should disappear.

## Important Notes

- Always back up your database before making changes.
- Isolation level changes affect **all databases** on the server.
- Use `READ COMMITTED` for optimal Drupal performance.