When you upgrade servers that participate in a replication setup, the procedure for upgrading depends on the current server versions and the version to which you are upgrading.

This section applies to upgrading replication from older versions of MySQL to MySQL 5.1. A 4.0 server should be 4.0.3 or newer.

When you upgrade a master to 5.1 from an earlier MySQL release series, you should first ensure that all the slaves of this master are using the same 5.1.x release. If this is not the case, you should first upgrade the slaves. To upgrade each slave, shut it down, upgrade it to the appropriate 5.1.x version, restart it, and restart replication. The 5.1 slave is able to read the old relay logs written prior to the upgrade and to execute the statements they contain. Relay logs created by the slave after the upgrade are in 5.1 format.

After the slaves have been upgraded, shut down the master, upgrade it to the same 5.1.x release as the slaves, and restart it. The 5.1 master is able to read the old binary logs written prior to the upgrade and to send them to the 5.1 slaves. The slaves recognize the old format and handle it properly. Binary logs created by the master subsequent to the upgrade are in 5.1 format. These too are recognized by the 5.1 slaves.

In other words, when upgrading to MySQL 5.1, the slaves must be MySQL 5.1 before you can upgrade the master to 5.1. Note that downgrading from 5.1 to older versions does not work so simply: You must ensure that any 5.1 binary log or relay log has been fully processed, so that you can remove it before proceeding with the downgrade.

Downgrading a replication setup to a previous version cannot be done once you have switched from statement-based to row-based replication, and after the first row-based statement has been written to the binlog. See Section 16.1.2, “Replication Formats”.

Some upgrades may require that you drop and re-create database objects when you move from one MySQL series to the next. For example, collation changes might require that table indexes be rebuilt. Such operations, if necessary, will be detailed at Section 2.4.1.1, “Upgrading from MySQL 5.0 to 5.1”. It is safest to perform these operations separately on the slaves and the master, and to disable replication of these operations from the master to the slave. To achieve this, use the following procedure: