Emergency

Options that make XtraDB tablespaces not compatible with MySQL

Expanded undo slots

Enabling innodb_extra_undoslots breaks compatibility with other programs. Specifically, it makes the datafiles unusable for ibbackup or for a MySQL server that is not run with this option.

Fast checksums

Enabling innodb_fast_checksum will use more CPU-efficient algorithm, based on 4-byte words which can be beneficial for some workloads. Once enabled, turning it off will require table to be dump/imported again, since it will fail to start on data files created when innodb_fast_checksums was enabled.

Page sizes other than 16KiB

This is controlled by variable innodb_page_size. Changing the page size for an existing database is not supported. Table will need to be dumped/imported again if compatibility with MySQL is required.

Relocation of the doublewrite buffer

Variable innodb_doublewrite_file provides an option to put the buffer on a dedicated disk in order to parallelize I/O activity on the buffer and on the tablespace. Only in case of crash recovery this variable cannot be changed, in all other cases it can be turned on/off without breaking compatibility.