Re: Problematic enforcement of "ERROR: functions in index predicate must be marked IMMUTABLE"

Kyotaro Horiguchi <horikyota.ntt@gmail.com> writes:
> Even given this, premising users keeping the volatility marks in line
> with the actual behavior of their corresponding functions, it might be
> benetifical to prohibit changes to the volatility category while it's
> being used for indices.

In the end, adding such restrictions would just give a false sense
of security, because there would always be gaps in whatever we did.
As you quote from the documentation, volatility markings are a promise
by the user to the system, not vice versa.  If you break your promise,
you get to keep both pieces of whatever trouble ensues.

                                                                            List of functions
 Schema | Name  | Result data type | Argument data types | Type | Volatility | Parallel |  Owner  | Security | Access privileges | Language | Internal name | Description
--------+-------+------------------+---------------------+------+------------+----------+---------+----------+-------------------+----------+---------------+-------------
 public | immut | text             |                     | func | immutable  | unsafe   | vagrant | invoker  |                   | plpgsql  |               |
(1 row)

postgres=# create or replace function immut() returns text as $$begin select 'one'; end; $$ language plpgsql;
CREATE FUNCTION
postgres=# \df+ immut
                                                                            List of functions
 Schema | Name  | Result data type | Argument data types | Type | Volatility | Parallel |  Owner  | Security | Access privileges | Language | Internal name | Description
--------+-------+------------------+---------------------+------+------------+----------+---------+----------+-------------------+----------+---------------+-------------
 public | immut | text             |                     | func | volatile   | unsafe   | vagrant | invoker  |                   | plpgsql  |               |
(1 row)