As a relational database, PostgreSQL provides a lot of features, and it is quite difficult to "scare" a PostgreSQL instance. In fact, a single instance can contain more than 4 billion individual databases, each with unlimited total size and capacity for more than 1 billion tables, each containing 32 TB of data. Moreover, if there's any concern that those upper limits won't suffice, please consider that a single table can have 1,600 columns, each 1 GB in size, with an unlimited number of multi-column (up to 32 columns) indexes. In short, PostgreSQL can store much more data than you can possibly think of!
Therefore, there is no amount of data that PostgreSQL cannot handle, but of course, in order to perform well with certain big databases, you need to understand PostgreSQL and its features.
PostgreSQL is fully ACID-compliant and has a very strong foundation in data integrity and concurrency. It ships with a procedural language, named PL/pgSQL...