As a general rule, to upgrade from one release series to another, you should go to the next series rather than skipping a series. To upgrade from a release series previous to MySQL 5.1, upgrade to each successive release series in turn until you have reached MySQL 5.1, and then proceed with the upgrade to MySQL 5.5. For example, if you currently are running MySQL 5.0 and wish to upgrade to a newer series, upgrade to MySQL 5.1 first before upgrading to 5.5, and so forth. For information on upgrading to MySQL 5.1, see the MySQL 5.1 Reference Manual.
There is a special case for upgrading to MySQL 5.5, which is that there was a short-lived MySQL 5.4 development series. This series is no longer being worked on, but to accommodate users of both series, this section includes one subsection for users upgrading from MySQL 5.1 to 5.5 and another for users upgrading from MySQL 5.4 to 5.5.
To upgrade to MySQL 5.5, use the items in the following checklist as a guide:
Before any upgrade, back up your databases, including the
mysqldatabase that contains the grant tables. See Section 6.2, “Database Backup Methods”.Read all the notes in Section 2.13.1.1, “Upgrading from MySQL 5.1 to 5.5”, or Section 2.13.1.2, “Upgrading from MySQL 5.4 to 5.5”, depending on whether you currently use MySQL 5.1 or 5.4. These notes enable you to identify upgrade issues that apply to your current MySQL installation. Some incompatibilities discussed in that section require your attention before upgrading. Others should be dealt with after upgrading.
Read Appendix D, MySQL Change History as well, which provides information about features that are new in MySQL 5.5 or differ from those found in earlier MySQL releases.
After upgrading to a new version of MySQL, run mysql_upgrade (see Section 4.4.7, “mysql_upgrade — Check Tables for MySQL Upgrade”). This program checks your tables, and attempts to repair them if necessary. It also updates your grant tables to make sure that they have the current structure so that you can take advantage of any new capabilities. (Some releases of MySQL introduce changes to the structure of the grant tables to add new privileges or features.)
mysql_upgrade does not upgrade the contents of the help tables. For upgrade instructions, see Section 5.1.8, “Server-Side Help”.
If you run MySQL Server on Windows, see Section 2.3.7, “Upgrading MySQL on Windows”.
If you use replication, see Section 17.4.3, “Upgrading a Replication Setup”, for information on upgrading your replication setup.
If you upgrade an installation originally produced by installing multiple RPM packages, it is best to upgrade all the packages, not just some. For example, if you previously installed the server and client RPMs, do not upgrade just the server RPM.
If you have created a user-defined function (UDF) with a given name and upgrade MySQL to a version that implements a new built-in function with the same name, the UDF becomes inaccessible. To correct this, use
DROP FUNCTIONto drop the UDF, and then useCREATE FUNCTIONto re-create the UDF with a different nonconflicting name. The same is true if the new version of MySQL implements a built-in function with the same name as an existing stored function. See Section 8.2.4, “Function Name Parsing and Resolution”, for the rules describing how the server interprets references to different kinds of functions.
You can always move the MySQL format files and data files between different versions on systems with the same architecture as long as you stay within versions for the same release series of MySQL.
If you are cautious about using new versions, you can always rename your old mysqld before installing a newer one. For example, if you are using a version of MySQL 5.1 and want to upgrade to 5.5, rename your current server from mysqld to mysqld-5.1. If your new mysqld then does something unexpected, you can simply shut it down and restart with your old mysqld.
If, after an upgrade, you experience problems with compiled client
programs, such as Commands out of sync or
unexpected core dumps, you probably have used old header or
library files when compiling your programs. In this case, you
should check the date for your mysql.h file
and libmysqlclient.a library to verify that
they are from the new MySQL distribution. If not, recompile your
programs with the new headers and libraries. Recompilation might
also be necessary for programs compiled against the shared client
library if the library major version number has changed (for
example from libmysqlclient.so.15 to
libmysqlclient.so.16.
If problems occur, such as that the new mysqld
server does not start or that you cannot connect without a
password, verify that you do not have an old
my.cnf file from your previous installation.
You can check this with the
--print-defaults option (for
example, mysqld --print-defaults). If this
command displays anything other than the program name, you have an
active my.cnf file that affects server or
client operation.
If your MySQL installation contains a large amount of data that
might take a long time to convert after an in-place upgrade, you
might find it useful to create a “dummy” database
instance for assessing what conversions might be needed and the
work involved to perform them. Make a copy of your MySQL instance
that contains a full copy of the mysql
database, plus all other databases without data. Run your upgrade
procedure on this dummy instance to see what actions might be
needed so that you can better evaluate the work involved when
performing actual data conversion on your original database
instance.
It is a good idea to rebuild and reinstall the Perl
DBD::mysql module whenever you install a new
release of MySQL. The same applies to other MySQL interfaces as
well, such as PHP mysql extensions and the
Python MySQLdb module.