[h-e-w] How do I get emacs to stop ignoring .log files in tab-completion?

[Michael Campbell]

Subject pretty much says it, but when I want to read a log file,
emacs won't tab-complete the name in the minibuffer.  What's worse, I
use log4j for a lot of things, ending up with a lot of timestamped
log files, and emacs will autocomplete to the timestamped version.

Where is the setting that tells it which file extensions to ignore
during tab-complete, so I can change that to my liking?

Thanks!