If you are planning to use PITR or if you want to use an XLOG archive to assist in your streaming setup, various things can go wrong, for example:
Pushing of the XLOG might fail
Cleanup of the archive might fail
Of course, there are countless other things that can go wrong. However, in this chapter, our goal is to focus on the most common issues people face.
A failing archive_command variable might be one of the greatest showstoppers in your setup. The purpose of archive_command is to push XLOG to some archive and store the data there. But what happens if those XLOG files cannot be pushed for some reason?
The answer is quite simple: the master has to keep these XLOG files to ensure that no XLOG files can be lost. There must always be an uninterrupted sequence of XLOG files. Even if a single file in the sequence of files is missing, your slave won't be able to recover anymore. For example, if your network has failed, the master will accumulate those...