When should I consider switching the Accelerator database from MySQL to Oracle or MSSQL?

We don't have any rigorous benchmarks, but I can tell you that we have users with thousands of agents running tens of thousands of builds per week with a MySQL backend. Generally the database itself is not a significant bottleneck, except when loading the "Builds" page in the cluster manager, which involves queries against the largest table in the database. In truth, we added support for Oracle and MSSQL not because of some problem with MySQL, but because some environments have standardized on those other databases, so they require us to integrate.

One thing to keep in mind is the need to perform regular maintenance on your database. In particular the `ec_build` and `ec_message` tables may accumulate a large amount of data. You should prune those regularly in order to avoid needlessly burdening your database with old information. The frequency with which you need to do this maintenance depends on the workload you perform with the cluster, and the capacity of your cluster manager server, of course. If you have a relatively light workload, or a particularly beefy CM, you may not need to prune very often at all.