Postgresql (via psql) seems to always auto commit after each statement unless a begin has been issued, in which case it commits on a commit/rollback. Fine.
But ODBC has an autocommit flag that says do it or don't. A mode on the transaction. That is a different model to using begins.
So how do they interact? Does ODBC autocommit actually send anything to the server, or does it just issue a hidden begin if set false? Suppose I have autocommit false, and then do
-- autocommit = false in ODBC driver
-- no explicit begin
update 1;
update 2;
rollback;
-- no begin
update 4;
update 5;
rollback;
does update 4 get rolled back? I presume that the others all do get rolled back.
Please, no responses that say auto commit auto commits after every query. This is a (relatively) sophisticated question.
Update 4 will get rolled back.
All clients that support "autocommit = off" implement that by sending an extra BEGIN to the server before the first statement after the end of a transaction. PostgreSQL itself is oblivious to that; it does not have a mode where autocommit is disabled.