If you are having a problem with load on the server, then using MySQL from another server could lower the load some. As far as how much change you will notice it really depends on how much of your load to begin with was from MySQL. With Ozzu, I would say a descent amount of the load does come from MySQL, and if Ozzu ever got busy enough it may very well be worth it to do the same thing and have a dedicated MySQL server, as well as a dedicated Apache server to serve the website.
Another thing you may want to consider instead of doing this, is to see if you can optimize the way your code is, and your SQL queries. At one time Ozzu was creating a enormous load on the server which much less traffic than it is now. Instead of throwing new hardware into the picture to resolve things, I went through every SQL statement and found the ones that were resource hogs. Rewriting and optimizing the queries can really make a difference. Another thing that helped a great deal was to properly use the right indexes on the MySQL tables so that lookups were much quicker. You can also utilize the MySQL slow query log to find queries that take too long which could cause MySQL to use more resources than it should. Eventually this could lead to running out of memory and having to swap to the hard drive which is extremely slow and causes really large loads. This was something Ozzu at one point had problems with in the past. After going through everything and making sure things were optimized, Ozzu has been able to grow without having to have multiple servers to run the website (yet anyway). I should note that Ozzu does offload all of its DNS to two dedicated DNS servers which does decrease the load slightly.
So overall if I were you I would look for ways to optimize first, and if you feel there is nothing else that can be done then consider breaking resources up between numerous servers. Hope this helps some.
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