Our company servers are currently hosted on a VPS and we've decided to move into dedicated servers.
When choosing the best hardware for a DB server, what should we invest more resources: better CPU (more cores)? or more RAM?
Where is the best ROI?
Any suggestions?
You should invest in both.
As for MySQL, if you are using InnoDB as your default storage engine, you must upgrade to MySQL 5.5 in order to use more cores. Here are some of my past posts on this subject
As a point of reference, I have a client at my employer's web hosting company that has three DB Servers in Circular Replication. Each DB server has the following:
They have had this setup for a whole year. I personally configured my.cnf for multicore engagement. All 12 CPUs are in use. The InnoDB Buffer Pool is full to capacity. There have been no complaints from the client on the DB Performance since this layout was setup for them.
Tuning InnoDB is very important because if you don't, MySQL 5.5 will perform worse than MySQL 5.1. In some cases, it can be worse than MySQL 4.1.
As for RAM, tuning connection usage, the number of connections and InnoDB caches is the most important thing
MySQL does not properly utilize CPUs with more than 4 cores, so you would go for 4-cores max, and as much RAM as you can get to be able to carry out as much of the processing in memory as possible.
