Re: Transform for pl/perl

On 6/6/18 12:14, Alvaro Herrera wrote:
> On 2018-May-17, Peter Eisentraut wrote:
> 
>> The items that are still open from the original email are:
>>
>> 2) jsonb scalar values are passed to the plperl function wrapped in not
>>    one, but _two_ layers of references
>>
>> 3) jsonb numeric values are passed as perl's NV (floating point) type,
>>    losing precision if they're integers that would fit in an IV or UV.
>>
>> #2 appears to be a quality of implementation issue without any
>> user-visible effects.
>>
>> #3 is an opportunity for future improvement, but works as intended right
>> now.
>>
>> I think patches for these issues could still be considered during beta,
>> but they are not release blockers IMO.
> 
> It appears to me that item #2 definitely would need to be fixed before
> release, so that it doesn't become a backwards-incompatibility later on.

The way I understand it, it's only how things are passed around
internally.  Nothing is noticeable externally, and so there is no
backward compatibility issue.

At least that's how I understand it.  So far this is only a claim by one
person.  I haven't seen anything conclusive about whether there is an
actual issue.

> I'm not sure I agree that #3 is just a future feature.  If you have
> functions working with jsonb numeric giving exact results, and later
> enable transforms for plperl, then your function starts giving inexact
> results?  Maybe I misunderstand the issue but this doesn't sound great.

It would be the other way around.  Right now, a transform from jsonb to
Perl would produce a float value in Perl.  The argument is that it could
be an integer value in Perl if the original value fits.  That's a change
worth considering, but the current behavior is consistent and works as
designed.

I took a brief look at this, and it seems there are some APIs needed to
be exposed from numeric.c to know whether a numeric is an integer.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
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