In database systems and computing systems in general, we have two ways to improve performance. The first one is to simply replace our servers with more powerful ones, keeping the same network topology and systems architecture. This is called vertical scaling.
An advantage of vertical scaling is that it is simple, from an operational standpoint, especially with cloud providers such as Amazon making it a matter of a few clicks to replace an m2.medium with an m2.extralarge server instance. Another advantage is that we don't need to make any code changes, and so there is little to no risk of something going catastrophically wrong.
The main disadvantage of vertical scaling is that there is a limit to it; we can only get servers that are as powerful as those that our cloud provider can give to us.
A related disadvantage is that getting more powerful servers...
