One habit some database deployments adopt that is counterproductive with PostgreSQL is the idea that the version of the software used should be frozen forever once the system is validated as working. This is a particularly troublesome viewpoint for systems that are running into performance issues to adopt. The performance increases you'll find just from upgrading from older to newer PostgreSQL versions can be far larger than anything you can do just by tweaking the older version. Similarly, if you're running into a problem with how a specific query is executing, don't be surprised to find that's fixed in a later version of PostgreSQL, and upgrading to it is really your only option to obtain that fix.
There are a few reasons for the feature by version list given below. One is to make you aware of what your version of PostgreSQL can and can't do from a performance perspective, information that can be hard to accumulate on your own (the release notes are...