I have been experimenting with adding filters to the Database Browser by substituting the tagnavi_user.config and tagnavi_custom.config files in place of the default tagnavi.config file, and I have discovered something that seems very surprising to me.
I have all of my music tracks in a directory named _otherLIBs at the root of my iPod's storage, and in "Settings->General Settings->Database->Select directories to scan" I have specified that directory as the only place where Rockbox should look for music files. After the database is initialized and built, I use Database->Track to display a list of all 3212 tracks in the database, which takes Rockbox about a full minute to accomplish. The instruction in tagnavi.config that Rockbox uses for that operation is:
"Track" -> title = "fmt_alphanum_title"
I edited that instruction to include the condition that each track to be listed must have a file (path) name that begins with the name of the _otherLIBs directory (which all of them do). So the instruction becomes:
"Track" -> title ? filename ^ "/_otherLIBs" -> title = "fmt_alphanum_title"
Using that edited instruction it takes Rockbox between one and two seconds (instead of a full minute) to display a list of all 3212 tracks in the database.
Is the logic [edit: not "logic", "mechanism"] behind this usage something that Rockbox could incorporate in some form to speed up some of its default operations?