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Subject: Re: Compiling GNATColl on Windows
Date: Tue, 16 Dec 2014 09:48:16 +0100
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Date: 2014-12-16T09:48:16+01:00
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On 2014-12-15 23:37, Dmitry A. Kazakov wrote:
> 
> Roughly same in ODBC:
> 
> declare
>    Environment : aliased ODBC_Environment;
>    Connection : aliased ODBC_Connection (Environment'Access);
> begin
>    Connect (Connection, "My_DB", "Myself", ...);
>    declare
>       Command : aliased ODBC_Command (Connection'Access);
>    begin
>       Prepare (Command, "SELECT COL1,COL2 FROM ...");
>       Execute (Command);
>       Fetch (Command);
>       Some_Variable := Get (Command'Access, 1, On_Error);
>       Some_Other_Variable := Get (Command'Access, 2, Always);
>    end;
> end;
> 
> No need to fiddle with cursors explicitly and nothing to commit, if only
> reading.


Actually you do need to fiddle with server-side cursors sometimes.
Like if you have a very large table and want to treat all rows.

I've got a simulation program that reads a table of 30_000_000 rows,
that are recordings from actual events since this June.

The simulation reads the data in timestamp order (which is a field in
the table) and tries different algorithms on the data.
The outcome is somewhat based on previous outcome, so I do not want
to split the recordset.

The one with best outcome survives ans is tried in real life later on.

But the table grows, and I expect it to be ca 33 M rows at the ens of
the year. And next year, if I record the whole year, I'll end up with
60M+ rows.

For that, I _really_ like cursors on the server side.
It seems like your ODBC reads the whole recordset into the clients memory?

Or do I misunderstand it?



--Björn