Couldn't execute 'FLUSH TABLES WITH READ LOCK’
Learn how to deal with the READ LOCK permission error, and why LOCK is needed on certain MySQL databases.
Background
When performing a database backup using SimpleBackups, you may encounter the following error:
Couldn't execute 'FLUSH TABLES WITH READ LOCK': Access denied for user 'admin'@'%' (using password: YES) (1045)
This error indicates that the specified user, admin in this case, lacks the necessary permissions to execute the FLUSH TABLES WITH READ LOCK command. This command is required to ensure data consistency during the backup process.
Resolving the Permission Issue
To grant the required permissions, you can execute the following SQL statements using a user with sufficient privileges:
SQL
GRANT RELOAD ON *.* TO 'admin'@'%';
FLUSH PRIVILEGES;
The GRANT RELOAD statement grants the RELOAD privilege to the admin user, allowing them to execute the FLUSH TABLES WITH READ LOCK command. The FLUSH PRIVILEGES statement ensures that the newly granted privilege takes effect immediately.
Database Locking Behavior
The behavior of database locking during a backup operation depends on the storage engine used for your tables.
- MyISAM: For MyISAM tables, the backup process acquires a global read lock on the entire database. This means that other processes, including queries and updates, will be blocked until the backup is complete.
- InnoDB: For InnoDB tables, the backup process does not acquire a global read lock. Instead, it uses a more granular locking mechanism that allows concurrent reads and writes to the database. However, there may still be some performance impact, especially for large databases.
Best Practices for Database Backups
- Use a Dedicated User: Create a dedicated user for backups with minimal privileges to reduce the risk of security breaches.
- Schedule Backups During Off-Peak Hours: To minimize impact on database performance, schedule backups during off-peak hours when database usage is low.