[Digikam-users] Some questions about digikam4.db

Gilles Caulier caulier.gilles at gmail.com
Thu Nov 10 10:02:01 GMT 2011

2011/11/9 Jean-Fran├žois Rabasse <jean-francois.rabasse at wanadoo.fr>

> 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".

yes, i know this, and we already talk with Marcel about.

I agree to move this data to another delegate DB file.

Please report this wish in a new bugzilla file.

> 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).

The thumbnail storing place used by Dolphin is defined in opendesktop
paper. digiKam support this rule in the past, and can support it if really
necessary as a compilation time option (look cmake configure option), but
this way is deprecated :

1/ PNG format is used to store thumbnail which space consuming (digiKam use
PGF format based on wavelets compression which is definitively better to
optimize space and speed)
2/ Storing place of thumbs is not configurable (digiKam thumbs DB can be).
It will fill your home directory
3/ We don't care about thumbs sharing, especially about dumy thumbs
generated by another application. digiKam thumbs generator is better in all
case (try to support all RAW files with dolphin for ex...)
4/ digiKam thumbs DB can handle removable media. OpenDesktop cannot do.

Gilles Caulier
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