Purge is essential for a MySQL database to clean up delete-marked table records and undo logs that are no longer needed for multiversion concurrency control (MVCC) or rollback operations.
The slow advancement of purge in the background compared to numerous data changes causes poor database performance.
InnoDB uses undo logs as the key data structure to support MVCC and rollback operations and purge to clean them up.
The most heavy-duty part of the purge operation is identifying delete-marked table records including those in clustered indexes, secondary indexes, and BLOB columns.
The number of purge threads, the workload characteristics, and database resource utilization can significantly impact the performance of purge operation.
Choosing the right instance class, partitioning and sharding strategies can improve the efficiency of the purge operation.
Using the schema_unused_indexes view in SYS schema to identify and drop the unused secondary indexes is a recommended optimization.
Monitoring and setting up alarms for the rollback segment history list length metric can warn of the need to optimize database capacity and workload characteristics.
Purge operation can be an essential tool to optimize a MySQL database's performance.
Optimizing purge operation needs careful consideration of workload optimization, database capacity planning, and configurations.