Q:

MySQL replication fails due to duplicate keys after master is restarted

I'm new to MySQL load balancing, I want to try the master-slave concept.
Whenever I setup master-slave for the first time, and both have up-to-date fresh data, that works perfectly fine. However,  whenever the master goes down, or I stop and then restart it, the slave starts generating errors because of duplicate keys.
Why would this be happening and how can I prevent this?
My application has a lot of update queries something like 5 SELECTs then 3 UPDATEs or INSERTs
My data will grow with time and I'm expecting quite a high load in the future.

A:

Don't stop a master while any slaves are connected to it. If you need to stop it, then stop the slaves first and the master at the end. This way, you won't have any errors like the one you described.

