Using digiKam with a LOT of tags

[Alexander Langley]

Hello digiKam Users,

digiKam Version: 5.4.0 (via Homebrew)
OS:              macOS
OS Version:      10.12.3 (Sierra)
PC Specs:        Intel core i5, 4GB RAM

I'm currently working on a project that requires I use a VERY LARGE number of
tags.  And by "VERY LARGE", I mean on the order of 220,000.  After reading the
digiKam database spec, I wrote a quick Python script to read my tag set in from
a source JSON document and add it to the digiKam database using the sqlite3
library. 

This did not make digiKam happy.  When I attempted to launch it after adding the
tags, it hung indefinitely at the loading screen step labeled "Reading the
Database..."  I verified that I hadn't mangled the database format, then tried
again, only to be met with the same hang.  By reducing the number of tags 85%
(33,000), I was able to convince digiKam to start again, but it took 10 minutes
for it to open...

Is this a supported use case?  Is there a box I can check somewhere to tweak
digiKam's database loading system to handle absurd numbers of tags?  If not,
would a code contribution to try to speed up tag loading be welcome?

- Alex