I have a PHP script that runs this query on Postgresql 7.2.3. Once it inserts the record in the e_catalog table it takes the id value and then inserts it in the e_catalog_cache table, the two tables must have the same rows and values.
I thought rhat inside a transaction block the subquery SELECT MAX(id) FROM e_catalog was safe from concurrent same transactions, that is the id value from SELECT MAX(id) FROM e_catalog was exactly that one inserted in the previous statement, but reading some threads in this mailing list I have some doubt now.
This is the query:

BEGIN WORK;
INSERT INTO e_catalog(id, name, descr) VALUES (nextval('sequence'), '$Name', '$Descr');

INSERT INTO e_catalog_cache(id, name, descr) VALUES ((SELECT MAX(id) FROM e_catalog), '$Name', '$Descr');

COMMIT WORK;

Thanks.