When downgrading to MySQL 5.5 from MySQL 5.6, keep in mind the following issues relating to behavior or features in MySQL 5.6 that differ in MySQL 5.5:
mysql.user table in MySQL 5.6 has a
password_expired column. The
mysql.user table in MySQL 5.5 does not.
This means that an account with an expired password in MySQL
5.6 will work normally in MySQL 5.5.
mysql.host table was removed in MySQL
5.6.7. When downgrading to a previous release, startup on
the downgraded server fails with an error if the
mysql.host table is not present. You can
recreate the table manually or restore it from a backup
taken prior to upgrading to MySQL 5.6.7 or higher.
TIMESTAMP columns, the
storage required for tables created before MySQL 5.6.4
differs from storage required for tables created in 5.6.4
and later. This is due to a change in 5.6.4 that permits
these temporal types to have a fractional part. To downgrade
to a version older than 5.6.4, dump affected tables with
mysqldump before downgrading, and reload
the tables after downgrading.
The following query identifies tables and columns that may
be affected by this problem. Some of them are system tables
mysql database (such as
proxies_priv). This means that
mysql is one of the databases you must
dump and reload, or server startup may fail after
SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME, DATA_TYPE FROM INFORMATION_SCHEMA.COLUMNS WHERE DATA_TYPE IN ('TIME','DATETIME','TIMESTAMP') ORDER BY TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME;
InnoDB search indexes (with a type of
FULLTEXT), introduced in MySQL 5.6.4, are
not compatible with earlier versions of MySQL, including
earlier releases in the 5.6 series. Drop such indexes before
performing a downgrade.
InnoDB small page sizes specified by the
configuration option, introduced in MySQL 5.6.4, are not
compatible with earlier versions of MySQL, including earlier
releases in the 5.6 series. Dump all
InnoDB tables in instances that use a
InnoDB page size, drop the
tables, and re-create and reload them after the downgrade.
As of MySQL 5.6, the
file contains a line count and a replication delay value, so
the file format differs from that in older versions. See
Section 18.104.22.168, “Slave Status Logs”. If you downgrade a
slave server to a version older than MySQL 5.6, the older
server will not read the file correctly. To address this,
modify the file in a text editor to delete the initial line
containing the number of lines.
Beginning with MySQL 5.6.6, the MySQL Server employs Version
2 binary log events when writing the binary log. Binary logs
written using Version 2 log events cannot by read by earlier
versions of MySQL Server. To generate a binary log that is
written using Version 1 log events readable by older
servers, start the MySQL 5.6.6 or later server using
which forces the server to employ Version 1 events when
writing the binary log.