To commit a prepared transaction, you must be either the same user that executed the transaction originally, or a superuser. But you do not have to be in the same session that executed the transaction.
This command cannot be executed inside a transaction block. The prepared transaction is committed immediately.
All currently available prepared transactions are listed in the pg_prepared_xacts system view.
Commit the transaction identified by the transaction identifier foobar :
COMMIT PREPARED 'foobar';