Re: Detection of nested function calls

Le 28/10/2013 09:39, Andres Freund a écrit :
> On 2013-10-28 09:13:06 +0100, Hugo Mercier wrote:
>> Le 25/10/2013 18:44, Tom Lane a écrit :
>>> Hugo Mercier <hugo(dot)mercier(at)oslandia(dot)com> writes:
>>>> Le 25/10/2013 17:20, Tom Lane a écrit :
>>>>> How do you tell the difference between

>>> The point I'm trying to make is that in the first case, foo would be
>>> receiving a first argument that was flat and a second that was not flat;
>>> while in the second case, it would be receiving a first argument that was
>>> not flat and a second that was flat. The expression labeling you're
>>> proposing does not help it tell the difference.
>>
>> No it does not. It's then up to the data type to store whether it is
>> flat or not. And every functions manipulating this type is assumed to be
>> aware of this flat/non-flat flagging.
>
> But what if the in-memory type contains pointers and is copied or
> spilled to disk? There needs to be a mechanism handling that case.

It must not happen. The 'nested' boolean may be seen as "everything
returning from this function may be stored on disk at any time, so
serialize it" for nested==0.

If there is another mechanism to tell, inside a function, if the result
will be "stored" (stored on disk, copied to another context, ...) or
not, then I'll be happy with that.

> I think we'd need another argument to CREATE FUNCTION like SERIALIZE
> pointing to a function that that has to return data that can be stored
> on disk. Deserialization would be up to individual functions.

Either as argument to CREATE FUNCTION or to CREATE TYPE, right ?

Ok, so a user function calls PG_DETOAST to get its input. The most
nested will get it straight from where it is stored.
Then the function can decide to deserialize it in its own format,
process it, and return it as is, with probably a call to
PG_RETURN(pointer). Nested function will get their inputs still from
PG_DETOAST and can use them directly.
But for the last function in the nesting chain, how the pointer will be
serialized back to something storeable ? i.e. who will call the
serialize function declared in CREATE (FUNCTION|TYPE) ?

--
Hugo Mercier
Oslandia