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From: Morris de Oryx <[email protected]>
To: pgsql-general <[email protected]>
Subject: Remedial C: Does an ltree GiST index *ever* set recheck to true?
Date: Fri, 30 Aug 2024 11:51:51 +1000
Message-ID: <CAKqnccgejE8E5xheLMd+pDtQ+nXiZHoGhf6yN3FsJ2_rtGzx2g@mail.gmail.com> (raw)

I'm trying to determine if an ltree GiST index search *ever *needs to load
a row out of heap for a recheck, of if the index entry itself includes
enough information for a definitive answer. I believe that this is
controlled by the recheck flag in the consistency function.

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.

https://github.com/postgres/postgres/blob/master/contrib/ltree/ltree_gist.c

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.)

Can anyone confirm or deny for me? I'd be grateful for the certainty.

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