Re: plans for PostgreSQL 12

On 04/06/18 09:37, Pavel Stehule wrote:
>
>
> 2018-06-04 9:24 GMT+02:00 Heikki Linnakangas <hlinnaka(at)iki(dot)fi
> <mailto:hlinnaka(at)iki(dot)fi>>:
>
> On 04/06/18 09:12, Pavel Stehule wrote:
>
> It requires introduction of new "safe" functions (& operators).
> Immutable
> functions are not enough safe.
>
> CREATE OR REPLACE FUNCTION public.fx()
>   RETURNS integer
>   LANGUAGE plpgsql
>   IMMUTABLE
> AS $function$
> BEGIN
>    RETURN (SELECT count(*) FROM pg_class);
> END;
> $function$
>
> postgres=# SELECT fx();
> ┌─────┐
> │ fx  │
> ╞═════╡
> │ 343 │
> └─────┘
> (1 row)
>
>
> That function is incorrectly marked as IMMUTABLE. In that situation,
> it's enough that we throw a sane error like "ERROR: no snapshot
> available".
>
> Yes, it is incorrect mark. Unfortunately - this is often workaround for
> wrong estimations - so I afraid, in this case, your proposed fix breaks
> lot of applications.

I would say such applications are already broken.
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