I have a library of about 22,000 music files. Initially, I was having problems processing the library. Lots of sqlite3 timeout issues.
Following the advice for sqlite3 from the URL below here seems to have resolved that bottleneck at least for metafile information.
sqlite3 /DataVolume/.wdcache/.plexmediaserver/Application Support/Plex Media Server/Plug-in Support/Databases/com.plexapp.plugins.library.db PRAGMA default_cache_size = 20000; ctrl-d