Abstraction can protect a database from even the busiest platform. At the time of writing this book, applications and web services often involve hundreds of servers. If we follow a simple and naïve development cycle where applications have direct access to the database, each of these servers may require dozens of connections per program, even with a small server pool that can result in hundreds or thousands of direct connections to the database. Is this what we want? Consider the scenario illustrated in the following diagram:

We need a way to avoid overwhelming the database with the needs of too many clients. As we suggested in the previous chapter, a PostgreSQL server experiences its best performance when the amount of active connections is less than three times the available CPU count. With a thousand incoming client connections, we will need hundreds of CPU cores to satisfy the formula.

Every incoming connection requires resources such as memory for query calculations and results...