<p>My question is a lot like <a href="https://stackoverflow.com/questions/80721/">this one</a>. However I'm on MySQL and I'm looking for the "lowest tech" solution that I can find. </p>

<p>The situation is that I have 2 databases that should have the same data in them but they are updated primarily when they are not able to contact each other. I suspect that there is some sort of clustering or master/slave thing that would be able to sync them just fine. However in my cases that is major overkill as this is just a scratch DB for my own use.</p>

<p>What is a good way to do this?</p>

<p>My current approach is to have a Federated table on one of them and, every so often, stuff the data over the wire to the other with an insert/select. It get a bit convoluted trying to deal with primary keys and what not. (<code>insert ignore</code> seems to not work correctly)</p>

<p>p.s. I can easily build a query that selects the rows to transfer.</p>

MySQL's inbuilt replication is very easy to set up and works well even when the DBs are disconnected most of the time. I'd say configuring this would be much simpler than any custom solution out there.
See
http://www.howtoforge.com/mysql_database_replication
for instructions, you should be up and running in 10-15 mins and you won't have to think about it again.
The only downside I can see is that it is asynchronous - ie. you must have one designated master that gets all the changes.