Re: PATCH: Add hstore_to_json()

On Fri, Dec 18, 2009 at 3:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>> Tom Lane escribió:
>>> Well, actually, now that you mention it: how much of a json type would
>>> be duplicative of the xml stuff?  Would it be sufficient to provide
>>> json <-> xml converters and let the latter type do all the heavy lifting?
>>> (If so, this patch ought to be hstore_to_xml instead.)
>
>> But then there's the matter of overhead: how much would be wasted by
>> transforming to XML, and then parsing the XML back to transform to JSON?
>
> Well, that would presumably happen only when sending data to or from the
> client.  It's not obvious that it would be much more expensive than the
> syntax checking you'd have to do anyway.
>
> If there's some reason to think that operating on json data would be
> much less expensive than operating on xml, there might be a case for
> having two distinct sets of operations internally, but I haven't heard
> anybody make that argument.

One problem is that there is not a single well-defined mapping between
these types. I would say generally that XML and YAML both have more
types of constructs than JSON. The obvious ways of translating an
arbitrary XML document to JSON are likely not to be what people want
in particular cases.

I think the performance argument is compelling, too, but we can't even
try benchmarking it unless we can define what we're even talking
about.

...Robert