The article describes idempotency keys and then completely misses making them the PK. The example is already using UUIDv4 as a PK, so they’re clearly not optimizing for performance. If you’re using the first 32 characters of a SHA256 hash, congratulations, store it as BINARY(8) / BYTEA - it’s even half the size of an encoded UUID, to boot.

Also, the DB will most certainly not silently ignore a unique constraint violation: it will send an error back. EDIT: unless you’re using INSERT OR IGNORE, of course.