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MySQL 8.0 Reference Manual
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MySQL 8.0 Reference Manual  /  The InnoDB Storage Engine  /  InnoDB and Online DDL

15.12 InnoDB and Online DDL

The online DDL feature permits in-place table alterations or concurrent DML, or both. Benefits of this feature include:

  • Improved responsiveness and availability in busy production environments, where making a table unavailable for minutes or hours is not practical.

  • The ability to adjust the balance between performance and concurrency during a DDL operations using the LOCK clause.

    • LOCK=EXCLUSIVE blocks access to the table entirely.

    • LOCK=SHARED allows queries but not DML.

    • LOCK=NONE allows full query and DML access to the table.

    • LOCK=DEFAULT or omitting the LOCK clause permits as much concurrency as possible depending on the type of DDL operation.

  • Avoidance of disk space usage and I/O overhead associated with copying the table and reconstructing secondary indexes.

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