If you have followed the advice in the previous chapters for doing all your database access through functions, you are in a great position to scale your database by horizontally distributing the data over multiple servers, also known as database sharding. Horizontal distribution means that you keep just a portion of a table on each partition of the database, and that you have a method to automatically access the right database when accessing the data.

We will gently introduce the concepts leading to the PL/Proxy partitioning language, and then delve into the syntax and proper usage of the language itself. Let's start with writing a scalable application from scratch. First, we will write it to be as highly performing as possible on one server. Then, we will scale it by spreading it out on several servers. We will first get this implemented in PL/Pythonu and then in PL/Proxy.