[Digikam-users] Digikam XMP schema ?

Jean-Fran├žois Rabasse jean-francois.rabasse at wanadoo.fr
Sun Feb 17 10:56:20 GMT 2013


Hi Volker,

On Sun, 17 Feb 2013, Volker Henn wrote:

> Hi, mysql is on the same machine.
>
> With sqlite I obseverd that obviously (no guarantee) when a single change is
> made, the whole database is written to hard disk. Then read again, next change
> made, completely written again. This take lot of time, since I organize my
> pictures in directories instead with tags, so I always shift a lot of files.
> Mysql seems to have a better chache strategy. Nevertheless there are problems
> with DK / mysql and the database user must be root.

Well, in that case you're right. Doing important reorganisations leads to
important database activity. And SQLite3 is a light weight library without
all caching ans requests journaling strategies real RDBMS have.
In my previous comment, I intended mostly small actions (rating or tagging
an image, etc.)

For large operations (folders reorganisation, rereading metadata for many
images, etc.) it's slow and I also happened to have problems, crashes or
so. Not to be nervous, I took the habit to do that on a copy of database,
and I/O access to the SQLite file can be enhanced when using a ramdisk.
Linux supports that very well, so :
  - backup /.../digikam4.db to ... digikam3.db.backup
  - copy the file to ramdisk, /dev/shm/digikam4.db
  - start DK with option : --database-directory /dev/shm
  - work...
  - when all is ok, satisfying results, no corruptions, no crashes, copy
    the ramdisk file back to original place /.../digikam4.db
    (Before shutting down the computer:-)
In case of problem, just forget, nothing is lost.

Regards,
Jean-Fran├žois


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