[Digikam-users] Some questions about digikam4.db

[Jean-François Rabasse]

Sorry for the "second shoot" :)

I forgot to signal that, in my opinion, there's also another space
consuming table that doesn't really need to be backuped, it is the
ImageHaarMatrix table that contains patterns signatures for the
find duplicates function.

It's the same kind of issue that the images thumbnails, it's nothing
but "scratch data", because both can be rebuilt upon need via the
DK commands menus, "Rebuild Thumbnails" and "Rebuild Fingerprints".

It's not fundamental application data, just scratch data kept for
faster access. So it can be (or should be) either into a separate
db file or other solution.
Some KDE applications, e.g. the Dolphin files browser, use a dedicated 
directory for that $HOME/.thumbnails. And, from an application program
point of view, loading a small amount of data (a thumbnail image file
is usually 10 or 12 Kbytes) is faster from a disk file than via the
blob management of a RDBMS (that also access data on the disk, plus the
SQL and blob I/O overhead).

Jean-François