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c918299eab
This just removes an unnecessary foreign key constraint, where we
already do the garbage collection manually in the database service.
However, as part of getting here I tried a couple of other variants
along the way:
- Changing the order of the primary key from `(hash, blocklist_hash,
idx)` to `(blocklist_hash, idx, hash)` so that inserts would be
naturally ordered. However this requires a new index `on blocks (hash)`
so that we can still look up blocks by hash, and turns out to be
strictly worse than what we already have.
- Removing the primary key entirely and the `WITHOUT ROWID` to make it a
rowid table without any required order, and an index as above. This is
faster when the table is small, but becomes slower when it's large (due
to dual indexes I guess).
These are the benchmark results from current `main`, the second
alternative below ("Index(hash)") and this proposal that retains the
combined primary key ("combined"). Overall it ends up being about 65%
faster.
<img width="764" height="452" alt="Screenshot 2025-08-29 at 14 36 28"
src="https://github.com/user-attachments/assets/bff3f9d1-916a-485f-91b7-b54b477f5aac"
/>
Ref #10264