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

On Wed, Nov 11, 2015 at 3:29 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> 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.

Fair enough, but I'm still not very interested in having something for
CustomScan only.

--
Robert Haas
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