Re: logical column ordering

From: Peter Eisentraut <peter_e(at)gmx(dot)net>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Cc: Phil Currier <pcurrier(at)gmail(dot)com>
Subject: Re: logical column ordering
Date: 2015-03-12 01:13:11
Message-ID: 5500E827.5000209@gmx.net
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On 12/9/14 12:41 PM, Alvaro Herrera wrote:
> To recap, this is based on the idea of having three numbers for each
> attribute rather than a single attnum; the first of these is attnum (a
> number that uniquely identifies an attribute since its inception and may
> or may not have any relationship to its storage position and the place
> it expands to through user interaction). The second is attphysnum,
> which indicates where it is stored in the physical structure. The third
> is attlognum, which indicates where it expands in "*", where must its
> values be placed in COPY or VALUES lists, etc --- the logical position
> as the user sees it.

Side idea: Let attnum be the logical number, introduce attphysnum as
the storage position, and add an oid to pg_attribute as the eternal
identifier.

That way you avoid breaking pretty much all user code that looks at
pg_attribute, which will probably do something like ORDER BY attnum.

Also, one could get rid of all sorts of ugly code that works around the
lack of an oid in pg_attribute, such as in the dependency tracking.

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