Re: Remedial C: Does an ltree GiST index *ever* set recheck to true?

Morris de Oryx <morrisdeoryx@gmail.com> writes:
> From what I've seen in the wild, and can sort out from the source, I think
> that ltree does *not* need to load rows from heap.

The comment in ltree_consistent is pretty definitive:

    /* All cases served by this function are exact */
    *recheck = false;

> I wonder because an ltree GiST index is "lossy" and this behavior is more
> like a lossless strategy. I think that's either because I've misunderstood
> what "lossy" means in this case, or it's because ltree GiST index *pages *are
> based on a signature (lossy), while ltree GiST index *leaf entries* contain
> the full tree/path (lossless.)

Yeah, the code is not terribly well commented but this bit in ltree.h
appears to be saying that leaf entries contain the original ltree:

 * type of index key for ltree. Tree are combined B-Tree and R-Tree
 * Storage:
 *    Leaf pages
 *        (len)(flag)(ltree)
 *    Non-Leaf
 *                 (len)(flag)(sign)(left_ltree)(right_ltree)
 *        ALLTRUE: (len)(flag)(left_ltree)(right_ltree)

and that seems consistent with the fact that ltree_consistent
does different things at leaf and non-leaf levels.

            regards, tom lane