Closes the last gap in databasev2 1; gives databasev2 3 its "before".
- `boot` mode: does NOTHING. WO_DATA replay runs before main, so a mode
with no work measures replay plus a fixed startup
- `replayseed N M`: N inserts + M updates — same live rows, longer log
- `replay` leg: empty-store startup floor measured and SUBTRACTED, then
two shapes timed, median of 3 boots each
- premise check: updates must actually append WAL records, else the two
shapes are one measurement and the penalty means nothing
- WAL bytes = non-zero prefix, never file size (fallocate'd to 1 MiB)
- per-record cost stored in NANOseconds: as us it rounded 5.5 and 5.3 to
6 and 5, too coarse for the number a checkpoint exists to improve
- 148 checks, 0 failures; gate bites on a doctored ns_per_record
Measured — same 20 000 live rows, different history:
- 20 000 records: 980 035 B WAL, 110 ms replay, 5.5 us/record
- 40 000 records: 1 960 035 B WAL, 211 ms replay, 5.3 us/record
- 1.9x boot cost for an IDENTICAL dataset; per-record cost flat, so
replay is linear in records not rows
- extrapolated: 10M records ~55 s of boot, 100M ~9 min
- databasev2 3 correction: it planned to use "22's aged-store replay
numbers", which never existed — 22 proved restart correctness, never
timed it
- databasev2 3 hazard recorded: compaction rewrites the log and moves
every record, so it invalidates every `resident: keys` offset — an
arbitrary byte in a rewritten file, not stale-but-readable
- databasev2 1 -> status: done
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
shoney.arickathil
5b1a8c96a1