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 MySQL 3.23 to 4.0 or 4.1. A 4.0 server should be 4.0.3 or newer, as mentioned in the section called “Replication Compatibility Between MySQL Versions”.
When you upgrade a master from MySQL 3.23 to MySQL 4.0 or 4.1, you should first ensure that all the slaves of this master are already at 4.0 or 4.1. If that is not the case, you should first upgrade your slaves: Shut down each one, upgrade it, restart it, and restart replication.
The upgrade can safely be done using the following procedure, assuming that you have a 3.23 master to upgrade and the slaves are 4.0 or 4.1. Note that after the master has been upgraded, you should not restart replication using any old 3.23 binary logs, because this will unfortunately confuse the 4.0 or 4.1 slave.
Block all updates on the master by issuing a FLUSH TABLES WITH READ LOCK statement.
Wait until all the slaves have caught up with all changes from the master server. Use SHOW MASTER STATUS on the master to obtain its current binary log file and position. Then, for each slave, use those values with a SELECT MASTER_POS_WAIT() statement. The statement will block on the slave and return when the slave has caught up. Then run STOP SLAVE on the slave.
Stop the master server and upgrade it to MySQL 4.0 or 4.1.
Restart the master server and record the name of its newly created binary log. You can obtain the name of the file by issuing a SHOW MASTER STATUS statement on the master. Then issue these statements on each slave:
mysql> CHANGE MASTER TO MASTER_LOG_FILE='binary_log_name',
-> MASTER_LOG_POS=4;
mysql> START SLAVE;
This section applies to upgrading replication from MySQL 3.23, 4.0, or 4.1 to 5.0.0. A 4.0 server should be 4.0.3 or newer, as mentioned in the section called “Replication Compatibility Between MySQL Versions”.
First, note that MySQL 5.0.0 is an alpha release. It is intended to work better than older versions (easier upgrade, replication of some important session variables such as sql_mode; see the section called “Changes in release 5.0.0 (22 Dec 2003: Alpha)”). However it has not yet been extensively tested. As with any alpha release, we recommend that you not use it in critical production environments yet.
When you upgrade a master from MySQL 3.23, 4.0, or 4.1 to 5.0.0, you should first ensure that all the slaves of this master are already 5.0.0. If that's not the case, you should first upgrade your slaves. To upgrade each slave, just shut it down, upgrade it to 5.0.0, restart it, and restart replication. The 5.0.0 slave will be able to read its old relay logs that were written before the upgrade and execute the statements they contain. Relay logs created by the slave after the upgrade will be in 5.0.0 format.
After the slaves have been upgraded, shut down your master, upgrade it to 5.0.0, and restart it. The 5.0.0 master will be able to read its old binary logs that were written before the upgrade and send them to the 5.0.0 slaves. The slaves will recognize the old format and handle it properly. Binary logs created by master after the upgrade will be in 5.0.0 format. These too will be recognized by the 5.0.0 slaves.
In other words, there are no measures to take when upgrading to 5.0.0, except that slaves must be 5.0.0 before you can upgrade the master to 5.0.0. Note that downgrading from 5.0.0 to older versions does not work so automatically: You must ensure that any 5.0.0 binary logs or relay logs have been fully processed, so that you can remove them before proceeding with the downgrade.