Performance and Concurrency Considerations for Online DDL

Performance and Concurrency Considerations for Online DDL
Online DDL improves several aspects of MySQL operation, such as performance, concurrency,
availability, and scalability:
• Because queries and DML operations on the table can proceed while the DDL is in progress,
applications that access the table are more responsive. Reduced locking and waiting for other
resources all throughout the MySQL server leads to greater scalability, even for operations not
involving the table being altered.
• For in-place operations, by avoiding the disk I/O and CPU cycles to rebuild the table, you minimize
the overall load on the database and maintain good performance and high throughput during the
DDL operation.
• For in-place operations, because less data is read into the buffer pool than if all the data was copied,
you avoid purging frequently accessed data from memory, which formerly could cause a temporary
performance dip after a DDL operation.
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