MySQL supports replication from one major version to the next higher major version. For example, you can replicate from a master running MySQL 4.1 to a slave running MySQL 5.0, from a master running MySQL 5.0 to a slave running MySQL 5.1, and so on.
However, one may encounter difficulties when replicating from an older master to a newer slave if the master uses statements or relies on behavior no longer supported in the version of MySQL used on the slave.
The use of more than 2 MySQL Server versions is not supported in replication setups involving multiple masters, regardless of the number of master or slave MySQL servers. This restriction applies not only to major versions, but to minor versions within the same major version as well. For example, if you are using a chained or circular replication setup, you cannot use MySQL 5.0.21, MySQL 5.0.22, and MySQL 5.0.24 concurrently, although you could use any 2 of these releases together.
In some cases, it is also possible to replicate between a master and a slave that is more than one major version newer than the master. However, there are known issues with trying to replicate from a master running MySQL 4.1 or earlier to a slave running MySQL 5.1 or later. To work around such problems, you can insert a MySQL server running an intermediate version between the two; for example, rather than replicating directly from a MySQL 4.1 master to a MySQL 5.1 slave, it is possible to replicate from a MySQL 4.1 server to a MySQL 5.0 server, and then from the MySQL 5.0 server to a MySQL 5.1 server.
It is strongly recommended to use the most recent release available within a given MySQL major version because replication (and other) capabilities are continually being improved. It is also recommended to upgrade masters and slaves that use early releases of a major version of MySQL to GA (production) releases when the latter become available for that major version.
Replication from newer masters to older slaves may be possible, but is generally not supported. This is due to a number of factors:
Binary log format changes.
The binary log format can change between major releases.
While we attempt to maintain backward-compatiblity, this is
not always possible. Major changes were made in MySQL 5.0.3
(for improvements to handling of character sets and
INFILE) and 5.0.4 (for improvements to handling of
time zones). Because of these changes, replication from a
MySQL 5.0.3 or later master to a MySQL 5.0.2 or earlier
slave is not supported. This also means that replication
from a MySQL 5.0.3 (or later) master to any MySQL 4.1 (or
earlier) slave is generally not supported.
This also has significant implications for upgrading replication servers; see Section 16.4.3, “Upgrading a Replication Setup”, for more information.
Use of row-based replication. Row-based replication was implemented in MySQL 5.1.5, so you cannot replicate using row-based replication from any MySQL 5.0 or later master to a slave older than MySQL 5.1.5.
Row-based replication is not available in MySQL 5.0. For more information about row-based replication in MySQL 5.1, see Replication Formats.
SQL incompatibilities. You cannot replicate from a newer master to an older slave using statement-based replication if the statements to be replicated use SQL features available on the master but not on the slave.
For more information on potential replication issues, see Section 16.4.1, “Replication Features and Issues”.