README/C-comment: document GiST's NSN value
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@ -92,10 +92,10 @@ index child page to be split between the time we make a queue entry for it
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(while visiting its parent page) and the time we actually reach and scan
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the child page. To avoid missing the entries that were moved to the right
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sibling, we detect whether a split has occurred by comparing the child
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page's NSN to the LSN that the parent had when visited. If it did, the
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sibling page is immediately added to the front of the queue, ensuring that
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its items will be scanned in the same order as if they were still on the
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original child page.
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page's NSN (node sequence number, a special-purpose LSN) to the LSN that
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the parent had when visited. If it did, the sibling page is immediately
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added to the front of the queue, ensuring that its items will be scanned
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in the same order as if they were still on the original child page.
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As is usual in Postgres, the search algorithm only guarantees to find index
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entries that existed before the scan started; index entries added during
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@ -51,6 +51,7 @@
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#define F_HAS_GARBAGE (1 << 4) /* some tuples on the page are dead,
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* but not deleted yet */
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/* NSN - node sequence number, a special-purpose LSN */
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typedef XLogRecPtr GistNSN;
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/*
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