XA stands for “eXtended Architecture”, and is a standard created by The Open Group for distributed transaction processing. While MySQL 5.0 was the first version to support XA, MySQL 5.7 has removed major limitations, fixed a number of bugs, and increased overall test-case coverage.…
The MySQL 5.6.4 release introduced support for fractional values within the temporal datatypes: TIME, DATETIME, and TIMESTAMP. Hence the storage requirement and encoding differs for them in comparison to older (5.5 and earlier) temporal datatypes. The storage format for the temporal datatypes in the old format are not space efficient either, and recreating tables having both the new and old formats can be a long and tedious process.…
OPTIMIZE TABLE is a maintenance operation used to recover the disk space and improve IO efficiency. It is recommended that the operation is carried out under the cases noted in the optimize table documentation.
MySQL versions prior to MySQL 5.6.17 does not allow concurrent changes (inserts, updates, deletes) to the table when the OPTIMIZE TABLE operation is being performed on that table.…
The temporal datatypes ‘TIME/DATETIME/TIMESTAMP’ supports fractional values starting from MySQL 5.6.4 version. Hence the storage requirement and encoding differs in comparison to pre- MySQL 5.6.4 temporal datatypes.
As mentioned in the section ‘Upgrading from MySQL 5.5 to 5.6’,
http://dev.mysql.com/doc/refman/5.6/en/upgrading-from-previous-series.html
Once you have imported the pre-MySQL 5.6.4 tables, ‘ALTER TABLE’ allows creation of tables containing temporal columns of both mysql-5.5 and mysql-5.6 format.…