Re: IMMUTABLE and PARALLEL SAFE function markings

On 27/11/2018 01:40, Tom Lane wrote:
> Vik Fearing <vik(dot)fearing(at)2ndquadrant(dot)com> writes:
>> On 27/11/2018 01:13, Stephen Frost wrote:
>>> Parallel safe functions should be marked as such. Immutable functions
>>> should be marked as such. We should not assume that one implies the
>>> other, nor should we operate as if they do.
>
>> Yes we should! Unless you can produce a case where an immutable
>> function is not parallel safe.
>
> As far as that goes, I agree with the idea of adding an oprsanity test
> that shows any built-in functions that are immutable but not parallel
> safe, on the grounds Stephen mentioned: it's probably a mistake, and
> if it isn't, we can add that function to the expected output.
>
> I'm way less inclined to buy into the idea that it MUST be wrong, though.
> Immutability is a promise about result stability and lack of side effects,
> but it is not a promise about implementation details. There could be an
> implementation reason not to run something in a parallel worker. Off the
> top of my head, a possible example is "it's written in plfoo which hasn't
> yet been made to work correctly in parallel workers".

Now, see, that is an actual argument for making a difference. The other
arguments in this thread were not, so say I.
--
Vik Fearing +33 6 46 75 15 36
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