Re: Functions Immutable but not parallel safe?

On Wed, Apr 5, 2017 at 8:57 AM, Peter Eisentraut
<peter.eisentraut@2ndquadrant.com> wrote:
> On 11/24/16 18:13, Robert Haas wrote:
>>> I'm finding hard to imagine a reason why these might be unsafe, but
>>> failed. I do notice they're all only used in information_schema.
>>>
>>> Could it just perhaps be that these just missed the verification
>>> process the other functions went through to determine their parallel
>>> safety?
>> Yes, I think that's it.  I went through pg_proc.h, but never looked at
>> information_schema.sql.
>
> This hasn't been fixed yet.  It's easy to to, but taking a step back,
>
> - Is there any reason an immutable function (that is not lying about it)
> should be anything but parallel safe?

It certainly isn't very likely.  It's not outright impossible.  For
example, imagine a function that does a calculation which is
deterministic given the inputs but which creates and uses temporary
tables in the course of performing the calculation.  Because the
function performs writes, it's parallel-unsafe.

> - If so, could CREATE FUNCTION default it that way?

This could be done but I'm not sure whether it's wise to make the
default value for one parameter depend on another parameter.

> - Maybe add a check to opr_sanity to make sure the default set of
> functions is configured the way we want?

That seems like a good idea.

-- 
Robert Haas
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