Re: [gnome-db] Gradual retrieval of data

[Murray Cumming <murrayc murrayc com>]

On Tue, 2006-03-28 at 09:25 +0200, Vivien Malerba wrote:
> On 3/27/06, Murray Cumming <murrayc murrayc com> wrote:
> > If I do a gda_connection_execute_command() with
> > "SELECT * FROM sometable"
> > and sometable has a million records,
> >
> > will libgda get all the data for all the records, or will it only get
> > the data from the database when I actually do
> > gda_data_model_get_value_at()?
> 
> That depends on the API DBMS provides. Usually (and it's the case for
> the Postgres provider), the data resulting from such a query is
> transfered to the client memory and then the data model only really
> creates the GdaValues from that data when a
> gda_data_model_get_value_at() is called.
> 
> However this is not suitable for very large amounts of data. For this
> purpose I introduced data models for which data can only be retreived
> using an iterator. To be more precise, the values stored in a data
> model can:
> - either be accessed using only an iterator (no
> gda_data_model_get_value_at() then)
> - or both using gda_data_model_get_value_at() or iterators: these are
> "random access" data models
> 
> The way a data model can be accessed can be retreived using the
> gda_data_model_get_access_flags().
> 
> >
> > I am interested in the Postgres backend.
> 
> Now to answer your question properly, the postgres provider always
> returns random access data models.
> 
> I'm working on a modification of the API which will allow to specify
> which kind of data model the user want to be returned, and then small
> modifications to the providers will be required (using declared
> cursors in case of the postgres DBMS).
> 
> The code to specify the requested data model type will be in CVS later
> this week.

So "random access" means, or causes, "all data transferred over the
network at once".
and "iterators" means "data transferred on demand"
?

This sounds like a very useful feature of the new API. I will try the
new API again soon. Many thanks.

-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com
www.openismus.com