If called without an argument, this function commits the default
transaction of the default link. If the argument is a connection
identifier, the default transaction of the corresponding connection
will be committed. If the argument is a transaction identifier, the
corresponding transaction will be committed. The transaction context
will be retained, so statements executed from within this transaction
will not be invalidated.
Valori restituiti
Restituisce true in caso di successo, false in caso di fallimento.