Before downgrading from MySQL 5.5, review the changes described in this section. Some changes may require action before or after downgrading.
System Tables. The
mysql.proc.commentcolumn definition changed between MySQL 5.1 and 5.5. After downgrading from 5.5 to 5.1, this table is seen as corrupt and in need of repair. Running mysql_upgrade from the version of MySQL to which you downgraded (as documented in the downgrade procedures) reverts the
InnoDB. MySQL 5.5 uses
InnoDB Pluginas the built-in version of
InnoDB. MySQL 5.1 includes
InnoDB Pluginas of 5.1.38, but as an option that must be enabled explicitly. See the Release Notes for MySQL 5.1.38.
Tables partitioned by [LINEAR] KEY. MySQL 5.5 implements new functions used to calculate row placement for tables partitioned by
LINEAR KEY. Tables that were created using
LINEAR KEYpartitioning in MySQL 5.5 cannot be used by a MySQL 5.1 server. In MySQL 5.5.31 and later, you can downgrade such tables with
ALTER TABLE ... PARTITION BY ALGORITHM=1 [LINEAR] KEY (...)to make them compatible with MySQL 5.1.