- updates append a DELTA (class, id, field, value, back-pointer), not a
full row. The workload decides it: a product catalogue changes one
narrow field of a wide row on every order, so a full-row append would
rewrite every field to move one integer on a shop's hottest path
- the back-pointer keeps the id map at one slot per row, which is the
mode's whole premise; a map growing per update would defeat it
- ONE fold function, three callers (read, replay, compaction). Three
implementations of one rule is how they drift, and a fold that differs
between reading and replaying is a database that changes its mind at
boot. Named as the design's principal risk
- indexed columns MAY change: price is exactly what a catalogue indexes,
so forbidding it would be a restriction users meet immediately
- no chain cap, deliberately. Compaction already rewrites live rows, so
every checkpoint resets every chain, and deltas grow the log which
pulls the next checkpoint forward — the workload that lengthens chains
triggers the fold that shortens them
- the risk that accepts: one hot SKU under an otherwise quiet write
rate. Task 7's benchmark must include it
- supersedes the 2026-08-26 spec's one-line full-row Update sketch,
marked in place rather than left as a second design in the tree
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
(cherry picked from commit c9a88b05c4c62a5df13253686c990aaccc3f9cbb)
shoney.arickathil
04017aea26