Why do you keep making the same argument again? Yes, SQLite has the parts needed to build a (very poor) graph db. But it will never be as performant as something dedicated, because the data structures used in SQLite have terrible characteristics for the algorithms used in graph operations. I like SQLite a lot, but it targets a niche and graph operations is simply not that niche.

You're not understanding what I mean by locality in this context. I mean that the on-disk structure should approximate an array of indexes, e.g.:

  const unsigned *edge_indexes = (const unsigned *) mmaped_structure_on_disk[disk_offsets[index]];

That's not the same as just being able to access those via an API; locality in this case means that you shouldn't need extra seeks for every single value, nor have to make a bunch of round trips through SQL.

That is the primary difference between traditional relational databases and column-oriented databases. Normal relational databases have row-based locality; column-oriented databases have column-based locality.