Date: Thu, 17 May 2018 17:11:23 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Dagfinn Ilmari =?iso-8859-1?Q?Manns=E5ker?= <ilmari@ilmari.org>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	Pavel Stehule <pavel.stehule@gmail.com>,
	Nikita Glukhov <n.gluhov@postgrespro.ru>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Transform for pl/perl
Message-ID: <20180517211123.wrml3yvrl3b2rmrq@alvherre.pgsql>
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Hello

This is still listed as an open item, though the patch proposed by Peter
upthread has been committed.  If I understand correctly, ilmari was
going to propose another patch.  Or is the right course of action to set
the open item as resolved?


On 2018-May-02, Dagfinn Ilmari Mannsåker wrote:

> Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:
> 
> > These two items are now outstanding:
> >
> > On 4/10/18 07:33, Dagfinn Ilmari Mannsåker wrote:
> >> 2) jsonb scalar values are passed to the plperl function wrapped in not
> >>    one, but _two_ layers of references
> >
> > I don't understand this one, or why it's a problem, or what to do about it.
> 
> It means that if you call a jsonb-transforming pl/perl function like
> 
>    select somefunc(jsonb '42');
> 
> it receives not the scalar 42, but reference to a reference to the
> scalar (**int instead of an int, in C terms).  This is not caught by the
> current round-trip tests because the output transform automatically
> dereferences any number of references on the way out again.
> 
> The fix is to reshuffle the newRV() calls in Jsonb_to_SV() and
> jsonb_to_plperl().  I am working on a patch (and improved tests) for
> this, but have not have had time to finish it yet.  I hope be able to in
> the next week or so.
> 
> >> 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.
> >
> > This seems fixable, but perhaps we need to think through whether this
> > will result in other strange behaviors.
> 
> Nubers > 2⁵³ are not "interoperable" in the sense of the JSON spec,
> because JavaScript only has doubles, but it seems desirable to preserve
> whatever precision one reasonably can, and I can't think of any
> downsides.  We already support the full numeric range when processing
> JSONB in SQL, it's just in the PL/Perl transform (and possibly
> PL/Python, I didn't look) we're losing precision.
> 
> Perl can also be configured to use long double or __float128 (via
> libquadmath) for its NV type, but I think preserving 64bit integers when
> building against a Perl with a 64bit integer type would be sufficient.
> 
> - ilmari
> -- 
> "The surreality of the universe tends towards a maximum" -- Skud's Law
> "Never formulate a law or axiom that you're not prepared to live with
>  the consequences of."                              -- Skud's Meta-Law
> 


-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services