Re: [GENERAL] Floating point error

From: Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
To: "Abhijit Menon-Sen *EXTERN*" <ams(at)2ndQuadrant(dot)com>
Cc: Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>, Daniel Farina <daniel(at)heroku(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Tom Duffey <tduffey(at)trillitech(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [GENERAL] Floating point error
Date: 2013-06-24 10:16:33
Message-ID: A737B7A37273E048B164557ADEF4A58B17BB5D38@ntex2010a.host.magwien.gv.at
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Abhijit Menon-Sen wrote:
> Sorry to nitpick, but I don't like that either, on the grounds that if I
> had been in Tom Duffey's place, this addition to the docs wouldn't help
> me to understand and resolve the problem.
>
> I'm not entirely convinced that any brief mention of extra_float_digits
> would suffice, but here's a proposed rewording:
>
> The <xref linkend="guc-extra-float-digits"> setting controls the
> number of extra significant digits included when a floating point
> value is converted to text for output. With the default value of
> <literal>0</literal>, the output is portable to every platform
> supported by PostgreSQL. Increasing it will produce output that
> is closer to the stored value, but may be unportable.
>
> It's a pretty generic sort of warning, but maybe it would help?

If I understood the original complaint right, anything that gives you
a hint that the textual representation is "truncated" would be helpful.

I like your suggestion and elaborated it a little.

What do you think of the attached version?

Yours,
Laurenz Albe

Attachment Content-Type Size
float-3.patch application/octet-stream 1.5 KB

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