Example Codes for mysqldump on AWS RDS (Linux)

• mysqldump: This is a command-line tool used to create backups (dumps) of MySQL or MariaDB databases.
• AWS RDS (Relational Database Service): It's a managed database service offered by Amazon Web Services (AWS) that runs MySQL or MariaDB.
• flush tables error: This occurs when mysqldump attempts to execute a statement called FLUSH TABLES WITH READ LOCK on an AWS RDS instance. This statement aims to lock all tables in the database, preventing any modifications while the dump is being created.
• Linux-specific: While the error might seem general, it primarily manifests on Linux systems when using mysqldump with AWS RDS.

Why the Error Happens on Linux with AWS RDS:

1. Security Restrictions: AWS RDS enforces security measures that limit user privileges. The standard mysqldump user on RDS doesn't have the SUPER privilege required for FLUSH TABLES WITH READ LOCK.
2. --master-data Option: If you're using the --master-data option with mysqldump, it tries to capture binary log coordinates for replication purposes. This option internally triggers the FLUSH TABLES WITH READ LOCK statement, leading to the error on RDS.
3. Potential Bug: In some older MySQL/MariaDB versions (particularly 5.7), there might have been a bug that caused mysqldump to attempt FLUSH TABLES WITH READ LOCK even without --master-data.

Resolving the Error:

Here are several approaches to address this issue:

1. Remove --master-data (if not required): If you don't need binary log coordinates for replication, omit the --master-data option from your mysqldump command. This eliminates the attempt to lock tables.
2. Upgrade mysqldump (if applicable): If you're using an older MySQL/MariaDB version, consider upgrading to a newer one (like 8.0.33 or later) that might have resolved the bug related to FLUSH TABLES WITH READ LOCK.
3. Use --single-transaction with Caution (RDS-specific): In MySQL 8.0.32 and later, if gtid_mode (Global Transaction Identifiers mode) is enabled on your RDS instance and you're using --single-transaction, you might need the RELOAD or FLUSH_TABLES privilege for mysqldump to work correctly. However, granting these privileges on RDS is generally not recommended due to security implications.

Additional Considerations for MariaDB:

While the core issue applies to both MySQL and MariaDB, keep in mind that MariaDB might have slightly different behaviors or privilege requirements. It's always best to consult the official MariaDB documentation for specific details.

Example Codes for mysqldump on AWS RDS (Linux)

Basic Dump (without --master-data):

mysqldump -u username -p database_name > database_dump.sql

• Replace username with your actual RDS database username.
• Replace database_name with the name of the database you want to dump.
• This command omits the --master-data option, avoiding the flush tables attempt.

Upgrading mysqldump (if possible):

Upgrade your MySQL/MariaDB client on your Linux system using your distribution's package manager (e.g., apt, yum). This might resolve the bug related to FLUSH TABLES WITH READ LOCK in older versions. Consult your distribution's documentation for specific upgrade instructions.

Using --single-transaction with Caution (RDS-specific):

WARNING: Granting RELOAD or FLUSH_TABLES privileges on RDS is not recommended due to security implications. Only use this approach if absolutely necessary and understand the risks.

mysqldump -u username -p --single-transaction database_name > database_dump.sql

• Important: This method assumes you have already granted the RELOAD or FLUSH_TABLES privilege to the mysqldump user on your RDS instance (not recommended).
• Use this approach with caution and only if the previous methods don't work for your specific scenario.

Additional Notes:

• Remember to replace placeholders (username, database_name) with your actual values.
• Secure your database credentials properly. Avoid storing them directly in scripts. Consider environment variables or a password manager.
• Always back up your data before performing any database operations.

Choosing the Right Method:

• The first example (without --master-data) is generally the safest and recommended approach.
• Upgrade mysqldump if you're confident about doing so and have an older version.
• The third example using --single-transaction should be a last resort due to security concerns.

• AWS RDS Snapshots: This built-in AWS RDS feature allows you to create point-in-time backups of your entire database instance. You can schedule automated snapshots at regular intervals or create them manually.
• mysqldump from Snapshot Restore: While not a direct mysqldump method, you can leverage RDS snapshots for backups. Restore the snapshot to a temporary RDS instance and then use mysqldump on that temporary instance to extract the desired database schema and data. This approach provides a complete database backup without requiring FLUSH TABLES.

mysqldump with mysqld_safe (Advanced):

• mysqld_safe: This is a utility used for managing MySQL/MariaDB server startup and shutdown.
• Advanced Technique: This method involves using mysqld_safe to start a temporary MySQL server instance on your Linux system, importing the database from your RDS instance, and then using mysqldump on the local server to create the backup. This approach bypasses the RDS security restrictions that prevent FLUSH TABLES on the actual RDS instance.

Important Considerations for mysqld_safe Method:

• This technique is more complex and requires a deeper understanding of MySQL/MariaDB server administration.
• Ensure proper configuration of the temporary server instance, including security settings.
• Not recommended for production environments unless you're comfortable with the advanced steps involved.

• RDS Snapshots: This is a robust and straightforward option for creating scheduled backups, especially if you need a complete database image.
• mysqldump with mysqld_safe: Consider this method only if you need more granular control over the backup process and understand the advanced steps involved.

Additional Recommendations:

• Regularly test your backup and restore procedures to ensure they function as expected.
• Explore managed database backup solutions offered by AWS or third-party providers for a more automated and centralized approach.