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    Great article! I think the explanation of leaf vs interior pages might have benefitted from a diagram. My understanding after reading it is this:

                            3───────┐
                            │pk data│
                1───────┐ ┌─┤A  ....│
                │rng ptr│ │ │B  ....│
              ┌─┤A-B 3  ├─┤ 4───────┤
              │ │C-D 4  │ │ │pk data│
    0───────┐ │ └───────┘ └─┤C  ....│
    │rng ptr│ │             │D  ....│
    │A-D 1  ├─┤             5───────┤
    │E-H 2  │ │             │pk data│
    └───────┘ │ 2───────┐ ┌─┤E  ....│
              │ │rng ptr│ │ │F  ....│
              └─┤E-F 5  ├─┤ 6───────┤
                │G-H 6  │ │ │pk data│
                └───────┘ └─┤G  ....│
                            │H  ....│
                            └───────┘
    

    (also reading https://www.sqlite.org/fileformat.html says that the row’s rowid will be used as the B+Tree page key instead of the PK, but I assume that’s a simplification on the article’s part because an integer PK will be used as the rowid. So assume the PKs in the above diagram are octodecimal :-) )

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      You are correct by default, however SQLite also has WITHOUT ROWID to use the actual primary key as the page key.