Just to be clear, are you referring to the single com.plexapp.plugins.library.db file; given your wording, I assume that’s the case. If so, that’s likely way, way too big. You may be affected by the database bloat problem that occurred over the summer. (I don’t have a link to the thread where it was discussed handy, but I’ll try to track it down.)
The issue caused massive database bloat (at least a couple of orders of magnitude above what it should be) and resulted in several issues, including database corruption.
Chuck’s utility is capable of correcting this bloat and checking for database corruption. While it is technically a 3rd-party project, it has been trusted by countless members of these forums. It’s also a script, so it’s not opaque (you have access to the source) and is run from the CLI.
[Edit]
I found the thread:
Note that it while it only describes a doubling of the database in the title, it was found to be much, much more severe as the thread grew.
