Savepoint

[koichi-szk]

Original Feature request #57, by Koichi Suzuki, 2012-06-12.

See sourceforge feature request for details.

XC need to support SAVEPOINT. It is not only for general application but also to support many GUI applications such as Access and Openoffice/Libreoffice. They use SAVEPOINT to implement "undo".

[koichi-szk]

Comment from Amit Khandekar:

Basically we should handle subtransactions correctly to support savepoints.
Another area which uses subtransactions is the exception block in PL languages. pl/pgsql uses subtransactions to implement exception blocks. That's probably why these no not work currently:

CREATE or replace FUNCTION merge_db(key INT, data TEXT) RETURNS VOID AS
$$
BEGIN
-- first try to insert the key
-- if we get a unique-key failure, update the record with new data
BEGIN 
INSERT INTO db(a,b) VALUES (key, data);
EXCEPTION WHEN unique_violation THEN
UPDATE db SET b = data WHERE a = key;
END; 
END; 
$$
LANGUAGE plpgsql;
SELECT merge_db(1, 'david');
SELECT merge_db(1, 'john');

The above should insert 'david', and then update the same record with 'john'. This is not working in XC.