Deciding on a version number

The first thing to work on when installing PostgreSQL is to decide on the version number. In general, a PostgreSQL version number consists of three digits. Here are some examples:

The last digit is the so-called minor release. When a new minor release is issued, it generally means that some bugs have been fixed (for example, some time zone changes, crashes, and so on). There will never be new features, missing functions, or changes of that sort in a minor release. The same applies to something truly important—the storage format. It won't change with a new minor release.

These little facts have a wide range of consequences. As the binary format and the functionality are unchanged, you can simply upgrade your binaries, restart PostgreSQL, and enjoy your improved minor release.

When the digit in the middle changes, things get a bit more complex. A changing middle digit is called a major release. It usually happens around once a year and provides you with significant new functionality. If this happens, we cannot just stop or start the database anymore to replace the binaries. In this case, we face a real migration process, which will be discussed later on in this book.

If the first digit changes, something really important has happened. Examples of such important events were introductions of SQL (6.0), the Windows port (8.0), streaming replication (9.0), and so on. Technically, there is no difference between the first and the second digit—they mean the same thing to the end user. However, a migration process is needed.

The question that now arises is this: if you have a choice, which version of PostgreSQL should you use? Well, in general, it is a good idea to take the latest stable release. In PostgreSQL, every version number following the design patterns I just outlined is a stable release.