Re: WIP Patch: Add a function that returns binary JSONB as a bytea

On 10/31/2018 10:21 AM, Tom Lane wrote:
> Stephen Frost  writes:
>> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>>> I dunno, I do not think it's a great idea to expose jsonb's internal
>>> format to the world.  We intentionally did not do that when the type
>>> was first defined --- that's why its binary I/O format isn't already
>>> like this --- and I don't see that the tradeoffs have changed since then.
>> I disagree- it's awfully expensive to go back and forth between string
>> and a proper representation.
> Has anyone put any effort into making jsonb_out() faster?  I think that
> that would be way more productive.  Nobody is going to want to write
> code to convert jsonb's internal form into whatever their application
> uses; particularly not dealing with numeric fields.
>
> In any case, the approach proposed in this patch seems like the worst
> of all possible worlds: it's inconsistent and we get zero benefit from
> having thrown away our information-hiding.  If we're going to expose the
> internal format, let's just change the definition of the type's binary
> I/O format, thereby getting a win for purposes like COPY BINARY as well.
> We'd need to ensure that jsonb_recv could tell whether it was seeing the
> old or new format, but at worst that'd require prepending a header of
> some sort.  (In practice, I suspect we'd end up with a wire-format
> definition that isn't exactly the bits-on-disk, but something easily
> convertible to/from that and more easily verifiable by jsonb_recv.
> Numeric subfields, for instance, ought to match the numeric wire
> format, which IIRC isn't exactly the bits-on-disk either.)
>
> 	


jsonb_send() sends a version number byte, currently 1. So if we invent a 
new version we would send 2 and teach jsonb_recv to be able to handle 
both. This was kinda anticipated.

I agree that just sending a blob of the internal format isn't a great idea.

cheers

andrew

-- 
Andrew Dunstan                https://www.2ndQuadrant.com
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