Mastering PostgreSQL 9.6

Using functions and transactions

As you know, everything that PostgreSQL exposes in user land is a transaction. The same, of course, applies if you are writing stored procedures. The procedure is always part of the transaction you are in. It is not autonomous—it is just like an operator or any other operation.

Here is an example:

test=# SELECT now(), mysum(id, id) FROM   generate_series(1, 3) AS id;               now              | mysum  -------------------------------+-------  2016-12-12 15:54:32.287027+01 |     2  2016-12-12 15:54:32.287027+01 |     4  2016-12-12 15:54:32.287027+01 |     6 (3 rows) 

All three function calls happen in the same transaction. This is important to understand because it implies that you cannot do too much transactional flow control inside a function. ...