Subject Gpre, Jdbc, and a Modest Proposal
Author Jim Starkey
I think it's time to talk about removing all dependencies on gpre and
gradually phase it out. It isn't feasible or desirable to drop it
altogether, but eliminating all internal use would a step forward.

The original idea behind gpre (and its DEC precursors) was that easy of
use came from tight language integration. A tight language integration
meant a preprocessor. And a preprecessor freed the API to
object/message based to make remote servers perform well, and BLR so the
compilation work could be done at preprocessor times, reducing amount of
runtime work. This is all well and good, but GDML lost and SQL won.

DSQL was designed as a quickie for a specific client, then productized.
Rather than inventing an API, I took the DB2 API lock, stock, and barrel
figuring no one was going to argue with IBM. The API stinks. Borland
moved the DSQL implementation from the client to the server without
fixing anything. I'm moving DSQL from the Y-valve into the engine where
it belongs. One of these days we can stop calling it DSQL and start
calling it just SQL.

The biggest problem with DSQL is that the API is close to unusable.
Anyone who could love SQLDAs could love MPE/XL.

I suggest that Firebird maintain the existing API, but select/design a
new API to gradually become the primary product API. I recommend that a
C++ binding be adopted. I implemented one in the OdbcJdbc project. A
representative piece of code:

PreparedStatement *statement = connection->prepareStatement (
"select * from RDB$RELATIONS where RDB$RELATION_ID=?");
statement->setInt (1, relationId);
ResultSet *resultSet = statement->executeQuery();

while (resultSet->next())
const char *relationName = resultSet->getString
printf ("Got one: %s\n", relationName);


The interface is semantically and almost syntactically identical to Java

There would be, over time, three implementations of the interface. One,
inside the engine, would be used in modules to replace the existing
pre-processed modules (met, dfw, ini, etc). Once complete, the engine
could be build without preprocessor.

The second implementation would be a client side library implemented
with the existing DSQL API. This already exists in OdbcJdbc and could
be rolled out with next to no effort.

The third implementation would be full integration of the interface into
the plumbing -- Y-valve, remote protocol, and engine. The third
implementation, however, would be completely transparent. The client
library would probe the Y-valve to see if it supported the new calls.
If so, it would attempt to route a call through the plumbing. If this
failed, it would do local emulation. This strategy would allow a
network to gradually shift over to the new API without breaking
anything. After a couple of reasons and due deliberation, the client
library could disappear completely in favor of full architectural
support of the new API.

A problem not addressed is non-OO languages that couldn't use JDBC
directly. A translation layer with handles would probably make most
sense, though the old API would remain in place for the indefinite future.

Over time, the internal implementation and the internal DSQL could
invert, with DSQL layered on JDBC rather than vice versa, backed up by a
pure SQL engine running in parallel to the legacy BLR engine.

None of this is going to happen as part of Vulcan, though I must admit
that dumping the internal gpre-ed modules is mighty tempting. But I do
think that this is a good time to discuss it.


Jim Starkey
Netfrastructure, Inc.
978 526-1376