How Can I Create an Index on a Large MySQL Production Table Without Disrupting Operations?

Creating an Index on a Large MySQL Production Table without Table Locking

Maintaining high availability during database maintenance is crucial, especially when dealing with hefty production tables. Adding an index to a table with millions of rows typically halts all data operations, causing significant service interruptions. Fortunately, several techniques allow you to create an index without blocking inserts and selects.

MySQL 5.6 and Later

In MySQL 5.6 and higher, index creation and deletion operations are performed online, ensuring that the table remains available for read and write operations during the process. However, this feature is not retroactive, meaning tables created using earlier MySQL versions will not benefit from this online indexing capability.

Using Circular Masters

If online indexing is not available, you can employ a circular master setup. This involves creating a secondary MySQL instance, replicating the production database to it, performing the schema update on the secondary instance, and atomically switching all clients to the updated instance. This method requires careful planning and coordination to avoid any data loss or inconsistencies.

Percona's pt-online-schema-change Tool

The pt-online-schema-change tool automates the circular master approach. It creates a temporary copy of the production table, updates the schema on the copy, synchronizes data using triggers, and seamlessly switches to the updated table. This tool offers a convenient alternative to manual schema changes with reduced downtime.

RDS Read Replica Promotion

If you are using MySQL through Amazon's RDS, you can take advantage of read replica promotion. This allows you to make schema changes on a read-only slave instance and then promote that instance to become the new master. While RDS simplifies the process, it still requires manual intervention to reconfigure and restart your applications and database.

Conclusion

Creating an index on a large production table without blocking inserts and selects is a challenge that requires careful consideration, and the best approach depends on the MySQL version and the availability of specialized tools and services. If you are using MySQL 5.6 or later, online indexing eliminates the need for table locks. Otherwise, techniques such as circular masters, pt-online-schema-change, or RDS read replica promotion offer ways to minimize service interruptions and maintain high availability during schema updates.

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