- 14.13.1 Online DDL Overview
- 14.13.2 Online DDL Performance, Concurrency, and Space Requirements
- 14.13.3 Online DDL SQL Syntax
- 14.13.4 Simplifying DDL Statements with Online DDL
- 14.13.5 Online DDL Implementation Details
- 14.13.6 Online DDL and Crash Recovery
- 14.13.7 Online DDL for Partitioned Tables
- 14.13.8 Online DDL Limitations
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=EXCLUSIVEblocks access to the table entirely.
LOCK=SHAREDallows queries but not DML.
LOCK=NONEallows full query and DML access to the table.
LOCK=DEFAULTor omitting the
LOCKclause 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.
The NDB Cluster
NDB storage engine also
supports online table schema changes, but uses its own syntax that
is not compatible with the syntax used for
online operations. For more information, see
Section 18.104.22.168, “ALTER TABLE Online Operations in NDB Cluster”.