Huge metadata.db file

Greetings.
I use calibre for conversion only and don't keep/store any books in it. I currently have 0 books. Yet my metadata.db file over 180 megabytes. Not that it's that big of an issue, but is this normal? And for someone who doesn't use it for storage, is there a way to shrink this without loosing my personal calibre preferences? I'm not entirely sure what exactly is in this file.
Thanks