Re: CustomScan in a larger structure (RE: CustomScan support on readfuncs.c)

On 2015-11-11 14:59:33 -0500, Robert Haas wrote:
> I don't see this as being a particularly good idea. The same issue
> exists for FDWs, and we're just living with it in that case.

It's absolutely horrible there. I don't see why that's a justification
for much. To deal with the lack of extensible copy/out/readfuncs I've
just had to copy the entirety of readfuncs.c into an extension. Or you
build replacements for those (as e.g. postgres_fdw essentially has
done).

> If we do want to improve it, I'm not sure this is the way to go,
> either. I think there could be other designs where we focus on making
> the serialization and deserialization options better, rather than
> letting people tack stuff onto the struct.

Just better serialization doesn't actually help all that much. Being
able to conveniently access data directly, i.e. as fields in a struct,
makes code rather more readable. And in many cases more
efficient. Having to serialize internal datastructures unconditionally,
just so copyfuncs.c works if actually used, makes for a fair amount of
inefficiency (forced deserialization, even when not copying) and uglier
code.

Andres