Slow TDB writing

[Zak Mc Kracken]

Hi all,

I've an application where exporting threads are producing Model 
instances of a pre-configured size, then I want to write those models 
into a TDB.

For the moment, I'm using this (I believe, rather canonical) code for 
the writing (dataSet is shared between threads:

        this.dataSet.begin ( ReadWrite.WRITE );
        try {
            Model dmodel = this.dataSet.getDefaultModel ();
            dmodel.add ( model );
            this.dataSet.commit ();
        }
        finally {
            this.dataSet.end ();
        }
It's extremely slow. When tested with about 2G of Turtle data, it is 
still running after hours. The same data exported to a .ttl and then 
loaded with tdbloader take a couple of minutes. Am I doing something 
wrong? Is the transactional approach inherently slower? Should I call 
the TDBLoader instead (the one used by the command line tool)?

Note that I'm OK to force everything to one thread only (or to serialise 
a couple of threads, as the code above seem to enforce), the application 
is going to be used in different export use cases and in some of them it 
will be truly parallel (eg, saving data on different files).

Thanks in advance for any help.

Marco.