Before getting started, the most important thing is to get an overview of the problem. Assuming that there is no corruption around, the first thing to do is to take a detailed look at the content of pg_stat_activity. As already outlined in this book, pg_stat_activity contains a list of all open database connections. There are a couple of things to look out for here:

Many middleware components open an insane number of database connections. Remember that each useless connection takes away a bit of memory, which could have been used for something more productive, such as caching. However, the number of database connections alone does not usually impose a dramatic overhead. The number of active snapshots is way more dangerous because active snapshots directly translate...