case SPI_ERROR_TRANSACTION:
				ereport(ERROR,
						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("cannot begin/end transactions in PL/pgSQL"),
						 errhint("Use a BEGIN block with an EXCEPTION clause instead.")));

create table tr01 (id serial, data text);

-- это не будет работать, вывалит ошибку типа 
-- ERROR:  SPI_execute_plan failed executing query "SAVEPOINT my_savepoint": SPI_ERROR_TRANSACTION
create or replace function tr_rlbk_01(_data text) returns bigint as $$
DECLARE _unused_id INT;
BEGIN
 SAVEPOINT my_savepoint;
 INSERT INTO tr01 (data) values (_data);
 _unused_id := currval('tr01_id_seq');
 ROLLBACK TO my_savepoint;
 RETURN _unused_id;
END$$ language 'plpgsql';
select tr_rlbk_01('Darn!');

-- трюк через использование EXCEPTION:
create or replace function tr_rlbk_02(_data text) returns bigint as $$
DECLARE _unused_id INT;
BEGIN
 INSERT INTO tr01 (data) values (_data);
 _unused_id := currval('tr01_id_seq');
 RAISE EXCEPTION 'rollbacking...';
EXCEPTION
 WHEN RAISE_EXCEPTION THEN -- отлов исключений порожденных именно через RAISE EXCEPTION
 RAISE NOTICE 'exception raised';
 RETURN _unused_id;
END$$ language 'plpgsql';
select tr_rlbk_02('Darn!'); -- работает