I just got to feel the downsides of trying to add mysql support to an app that was developed for sqlite exclusively first with digikam. Digikam has experimental mysql support so you can host your photos and the db on your NAS and access it from multiple computers.
I assume that digikam makes many simple queries for each individual photo when showing an overview page with thumbnails, tags and dates, as it's all stored in the db and notably slower than with sqlite. With GBit LAN it's acceptable, wifi makes you want to rip your hair out. It's not the bandwidth, but the latency. The sqlite case never made you consider to fetch multiple thumbnails in one query and now it's probably hard to redesign the whole thing to do that.
I assume that digikam makes many simple queries for each individual photo when showing an overview page with thumbnails, tags and dates, as it's all stored in the db and notably slower than with sqlite. With GBit LAN it's acceptable, wifi makes you want to rip your hair out. It's not the bandwidth, but the latency. The sqlite case never made you consider to fetch multiple thumbnails in one query and now it's probably hard to redesign the whole thing to do that.