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

As always, thanks very much for the confirmation.

On Fri, Aug 30, 2024 at 12:18 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Morris de Oryx <morrisdeoryx(at)gmail(dot)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
>