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@iki.fi
> <mailto:hlinnaka@iki.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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