Changes in MySQL 8.0 •With the introduction of the  --innodb-directories  feature, the location of file-per-table and general tablespace files created with an absolute path or in a location outside of the data directory should be added to the  innodb_directories  argument value. Otherwise,  InnoDB  is not able to locate these files during recovery. To view tablespace file locations, query the  INFORMATION_SCHEMA.FILES  table: •Undo logs can no longer reside in the system tablespace. In MySQL 8.0, undo logs reside in two undo tablespaces by default. For more information, see Section 15.6.3.4, “Undo Tablespaces” . • Incompatible change : As of MySQL 8.0.17, the  CREATE TABLESPACE ... ADD DATAFILE  clause does not permit circular directory references. For example, the circular directory reference ( /../ ) in the following statement is not permitted: •Due to a regression introduced in MySQL 8.0.14, in-place upgrade on a case-sensitive file system from MySQL 5.7 or a MySQL 8.0 release prior to MySQL 8.0.14 to MySQL 8.0.16 failed for instances with partitioned tables and  lower_case_table_names=1 . The failure was caused by a case mismatch issue related to partitioned table file names. The fix that introduced the regression was reverted, which permits upgrades to MySQL 8.0.17 from MySQL 5.7 or MySQL 8.0 releases prior to MySQL 8.0.14 to function as normal. However, the regression is still present in the MySQL 8.0.14, 8.0.15, and 8.0.16 releases. When upgrading from MySQL 5.7 to MySQL 8.0, any undo tablespaces that exist in the MySQL 5.7 instance are removed and replaced by two new default 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, undo tablespaces are created in the data directory. Upgrade from MySQL 5.7 to MySQL 8.0 requires a slow shutdown which ensures that undo tablespaces in the MySQL 5.7 instance are empty, permitting them to be removed safely. When upgrading to MySQL 8.0.14 or later from an earlier MySQL 8.0 release, undo tablespaces that exist in the pre-upgrade instance as a result of an  innodb_undo_tablespaces  setting greater than 2 are treated as user-defined undo tablespaces, which can be deactivated and dropped using  ALTER UNDO TABLESPACE  and  DROP UNDO TABLESPACE  syntax, respectively, after upgrading. Upgrade within the MySQL 8.0 release series may not always require a slow shutdown which means that existing undo tablespaces could contain undo logs. Therefore, existing undo tablespaces are not removed by the upgrade process. An exception to the restriction exists on Linux, where a circular directory reference is permitted if the preceding directory is a symbolic link. For example, the data file path in the example above is permitted if any_directory  is a symbolic link. (It is still permitted for data file paths to begin with ’ ../ ’.) To avoid upgrade issues, remove any circular directory references from tablespace data file paths before upgrading to MySQL 8.0.17 or higher. To inspect tablespace paths, query the INFORMATION_SCHEMA.INNODB_DATAFILES  table. In-place upgrade on a case-sensitive file system from MySQL 8.0.14, 8.0.15, or 8.0.16 to MySQL 8.0.17 fails with the following error when starting the server after upgrading binaries or packages to MySQL 8.0.17 if partitioned tables are present and  lower_case_table_names=1 : SELECT TABLESPACE_NAME, FILE_NAME FROM INFORMATION_SCHEMA.FILES \G CREATE TABLESPACE ts1 ADD DATAFILE ts1.ibd ’ any_directory /../ts1.ibd’; Upgrading from server version  version_number  with partitioned tables and lower_case_table_names == 1 on a case sensitive file system may cause issues, and is therefore prohibited. To upgrade anyway, restart the new server version with the command line option ’upgrade=FORCE’. When upgrade is completed, please execute ’RENAME TABLE  part_table_name TO  new_table_name ; RENAME TABLE  new_table_name TO  part_table_name ;’ for each of the partitioned tables. 275