Re: [gnome-db] Gradual retrieval of data

["Vivien Malerba" <vmalerba gmail com>]

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.

Cheers,

Vivien