Hardware is not always a problem. It might easily happen that you face something as simple as a power out. In general, PostgreSQL can easily survive power outs. The transaction log takes care of all failure-related issues, and with the help of xlog, it is always possible to bring the database back to a consistent state. It is safely possible to pull the plug and rely on the quality of PostgreSQL.

However, there are some nasty cases that can lead to even nastier troubles. On commit, PostgreSQL relies on the fact that data can be flushed to the disk. A system call, fsync, is used to ensure that everything relevant is forced to the disk. However, what happens if fsync cannot do its job? What if data cannot be (or data is not) flushed to the disk? If your system is up and running, everything is fine. The data will make it to the disk at some point, and life is good! However, what if a crash happens? The situation is grimmer. In short, anything can happen. If PostgreSQL...