> Unless you also have some triggers that repeatedly update the same rows,
> you do not have to commit every "n" inserts, it will not speed up anything.

I tried forcing commits only every 5k inserts (instead of after each
one), and achieve a 2.8x speed increase. I don't have any triggers. Do
you have more infos/url describing how firebird handles caching, commits
and disks I/O for personal knowledge ?

Thanks anyway everyone for your help.

--
Boris Herbinière-Sève