From: | Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net> |
Cc: | Kevin Van <kevinvan(at)shift(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: WIP Patch: Add a function that returns binary JSONB as a bytea |
Date: | 2018-10-31 15:13:13 |
Message-ID: | 841bfe52-2b9a-2d6e-50c2-3b3145a6dc3a@2ndQuadrant.com |
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Thread: | |
Lists: | pgsql-hackers |
On 10/31/2018 10:21 AM, Tom Lane wrote:
> Stephen Frost <sfrost(at)snowman(dot)net> writes:
>> * Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)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
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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