public inbox for [email protected]  

help / color / mirror / Atom feed

From: Morris de Oryx <[email protected]>
To: Tom Lane <[email protected]>
Cc: pgsql-general <[email protected]>
Subject: Re: Remedial C: Does an ltree GiST index *ever* set recheck to true?
Date: Fri, 30 Aug 2024 14:04:18 +1000
Message-ID: <CAKqnccjB0+Otzv7SxCLxWH0g=wqt4JR0osZD4j+dRWrbLhurRA@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
References: <CAKqnccgejE8E5xheLMd+pDtQ+nXiZHoGhf6yN3FsJ2_rtGzx2g@mail.gmail.com>
	<[email protected]>

As always, thanks very much for the confirmation.

On Fri, Aug 30, 2024 at 12:18 PM Tom Lane <[email protected]> wrote:

> Morris de Oryx <[email protected]> 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
>

view thread (2+ messages)

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected]
  Subject: Re: Remedial C: Does an ltree GiST index *ever* set recheck to true?
  In-Reply-To: <CAKqnccjB0+Otzv7SxCLxWH0g=wqt4JR0osZD4j+dRWrbLhurRA@mail.gmail.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox