Tablespaces •Default Undo Tablespaces •Undo Tablespace Size •Adding Undo Tablespaces •Dropping Undo Tablespaces •Moving Undo Tablespaces •Configuring the Number of Rollback Segments •Truncating Undo Tablespaces •Undo Tablespace Status Variables Default Undo Tablespaces Two default undo tablespaces are created when the MySQL instance is initialized. Default undo tablespaces are created at initialization time to provide a location for rollback segments that must exist before SQL statements can be accepted. A minimum of two undo tablespaces is required to support automated truncation of undo tablespaces. See Truncating Undo Tablespaces. Default undo tablespaces are created in the location defined by the  innodb_undo_directory  variable. If the  innodb_undo_directory  variable is undefined, default undo tablespaces are created in the data directory. Default undo tablespace data files are named  undo_001  and  undo_002 . The corresponding undo tablespace names defined in the data dictionary are  innodb_undo_001  and  innodb_undo_002 . As of MySQL 8.0.14, additional undo tablespaces can be created at runtime using SQL. See Adding Undo Tablespaces. Undo Tablespace Size Prior to MySQL 8.0.23, the initial size of an undo tablespace depends on the  innodb_page_size  value. For the default 16KB page size, the initial undo tablespace file size is 10MiB. For 4KB, 8KB, 32KB, and 64KB page sizes, the initial undo tablespace files sizes are 7MiB, 8MiB, 20MiB, and 40MiB, respectively. As of MySQL 8.0.23, the initial undo tablespace size is normally 16MiB. The initial size may differ when a new undo tablespace is created by a truncate operation. In this case, if the file extension size is larger than 16MB, and the previous file extension occurred within the last second, the new undo tablespace is created at a quarter of the size defined by the  innodb_max_undo_log_size  variable. Prior to MySQL 8.0.23, an undo tablespace is extended four extents at a time. From MySQL 8.0.23, an undo tablespace is extended by a minimum of 16MB. To handle aggressive growth, the file extension size is doubled if the previous file extension happened less than 0.1 seconds earlier. Doubling of the extension size can occur multiple times to a maximum of 256MB. If the previous file extension occurred more than 0.1 seconds earlier, the extension size is reduced by half, which can also occur multiple times, to a minimum of 16MB. If the  AUTOEXTEND_SIZE  option is defined for an undo tablespace, it is extended by the greater of the  AUTOEXTEND_SIZE  setting and the extension size determined by the logic described above. For information about the  AUTOEXTEND_SIZE  option, see Section 15.6.3.9, “Tablespace AUTOEXTEND_SIZE Configuration” . Because undo logs can become large during long-running transactions, creating additional undo tablespaces can help prevent individual undo tablespaces from becoming too large. As of MySQL 8.0.14, additional undo tablespaces can be created at runtime using  CREATE UNDO TABLESPACE  syntax. Adding Undo Tablespaces 3060