Bogus documentation for bogus geometric operators

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Bogus documentation for bogus geometric operators
Date: 2020-04-21 04:42:40
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While revising the docs for the geometric operators, I came across
these entries:

<^ Is below (allows touching)? circle '((0,0),1)' <^ circle '((0,5),1)'
>^ Is above (allows touching)? circle '((0,5),1)' >^ circle '((0,0),1)'

These have got more than a few problems:

1. There are no such operators for circles, so the examples are pure

2. What these operators do exist for is points (point_below, point_above
respectively) and boxes (box_below_eq, box_above_eq). However, the
stated behavior is not what the point functions actually do:

PG_RETURN_BOOL(FPlt(pt1->y, pt2->y));

PG_RETURN_BOOL(FPgt(pt1->y, pt2->y));

So point_below would be more accurately described as "is strictly below",
so its operator name really ought to be <<|. And point_above is "is
strictly above", so its operator name ought to be |>>.

3. The box functions do seem to be correctly documented:

PG_RETURN_BOOL(FPle(box1->high.y, box2->low.y));

PG_RETURN_BOOL(FPge(box1->low.y, box2->high.y));

But there are comments in the source code to the effect of

* box_below_eq and box_above_eq are obsolete versions that (probably
* erroneously) accept the equal-boundaries case. Since these are not
* in sync with the box_left and box_right code, they are deprecated and
* not supported in the PG 8.1 rtree operator class extension.

I'm not sure how seriously to take this deprecation comment, but it
is true that box_below (<<|) and box_above (|>>) have analogs for
other data types while these functions don't.

4. Just for extra fun, these point operators are listed in some
GIST and SP-GIST opclasses; though the box ones are not, as per
that code comment.

Perhaps it's too late in the v13 cycle to actually do anything
about this code-wise, but what should I do documentation-wise?
I'm certainly not eager to document that these operators behave
inconsistently depending on which type you're talking about.

regards, tom lane


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