Understanding Windows Installer Log Files
Windows Installer log files tend to be both verbose and cryptic. Richard Macdonald of the Windows Installer team at Microsoft has posted a great article in his blog to help developers understanding MSI logs. He starts with some general information how to activate logging and about the general syntax of the log file. But the best part in my opinion is the annotated log file he posted. I highly recommend reading his article:
There just one bit I'd like to add regading the log syntax. Richard explains what the lines tagged with (c) and (s) mean (client and server process, respectively), but there's a third tag: (N) for nested. Nested install custom actions are deprecated, but (N) also applies to the automatic uninstall of the old product version during a Major Upgrade.