One of the most asked questions is how to setup MySQL replication. The MySQL Reference Manual provides a good Replication How To as a starting guide on MySQL Replication 101.

MySQL replication has many uses including read scalability, backups, failover, online maintenance, upgrade testing and verification, software upgrades, alternative data or structure for performance queries and even benchmarking to name the popular uses.

When reviewing an installation of MySQL replication I use the following as part of my checklist of steps used for confirming your replication environment is operational.

Master Variables

• server-id – Replication will not work without this correctly set and unique
• log-bin – Pre-requisite for working replication

Kevin Burton wrote recently about why SHOW SLAVE STATUS is really not a good way to monitor how far behind your slave servers are, and how slave network timeouts can mess up the slave lag. I'd like to chime in and say this is exactly why I thought Jeremy Cole's MySQL Heartbeat script was such a natural fit for the MySQL Toolkit. It measures slave lag in a "show me the money" way: it looks for the effects of up-to-date replication, rather than asking the slave how far behind it thinks it is.

The slave doesn't even need to be