[Milhouse]

You make particular reference to client DBs, so what happens on the server machine?

The reason I ask is because, against the trend, I use path substitution for the Thumbnails folder. In Frodo.
(I know, I know, I don't get the performance, but man, does it make maintenance sooo much easier! Each new Pi on my network gets the same advancedsettings.xml thrown on an OpenELEC install - no fuss, no stress, and it just works! AFAIK, nothing pertaining to the media is stored on the Pi - it all comes from the server.)

If access is done via JSON, will Textures13.db still be relevant in my case?

I'm curious to see if I delete Textures13.db, whether or not XBMC will recreate it!

If you delete Textures13.db, XBMC will recreate it and slowly re-populate it with cached file details.

I'm not sure if XBMC will try to recreate the optimised artwork files, as it may realise there is already a matching file in the Thumbnails folder since you are sharing Thumbnails (this can lead to a problem where the new image won't replace the existing image). Then again, XBMC may just go right ahead and overwrite the existing Thumbnail file with the new version. Should XBMC overwrite existing files, and if the original artwork file has changed, this may leave your other clients with inconsistent information in their Textures13.db (image height, width etc. is all stored in the Textures13.db rather than extracted from the image each time). This can cause problems when those images are subsequently displayed with the incorrect image proportions.

Think of it like this: you're sharing everything (media library, Thumbnails) but not the "bridge" between your media library and the cached Thumbnails - that bridge is Textures13.db. Ideally, when sharing Thumbnails, you'd also have a single copy of Textures13.db on each client so that all clients would have a consistent "view" of the Thumbnails folder. Currently, this isn't really possible (maybe you could path-sub the Databases folder, but I wouldn't recommend it).

I'm not saying you're wrong to use path substitution to share Thumbnails, but it is a creaky solution that can fall apart quite easily. Deleting artwork from a shared Thumbnails folder is particularly problematic, as any clients that still have the deleted file referenced in their Textures13.db are likely to show a blank/default image.

This script is one alternative to path substitution as you can easily write a scheduled job that keeps all of your Pi clients and their local Textures13.db/Thumbnail caches up to date.