databasev2 4 part A, task 4. Scope extended with developer approval: the
plan authorised touching the sample only for observability, but no
existing leg has enough concurrent durable writes to exercise group
commit at all, so the payoff was unevaluable either way.
The finding that forced it:
- `mix` writes on one op in ten with C=4 (all_mode calls mix_mode(n/10,
4); Mixer writes on i % 10 == 9), so the quick run performs 20 writes
total. Measured mean batch 1.01 over 3112 barriers, peak 3
- that is a property of the WORKLOAD, not the mechanism: peak 3 of a
possible 4 shows batches form whenever writes actually coincide
- `wmix N C` added: every op a durable write, C at once. Updates rather
than inserts, so it is comparable to mixwrite and the row count stays
flat. Histogram kind 2 — a replayed store still holds the seeding run's
kind-0/1 Hist rows and merging those would report someone else's
latencies
- WO_WAL_STATS=1 prints one line at exit: batches, records, peak_batch,
peak_staged. Opt-in, because it would otherwise pollute every durable
program's output. Counters live in wo_wal; no builtin, the numbers are
diagnostic and not part of the language
Measured, and it scales with concurrency exactly as designed:
- C = 4 / 16 / 64 -> mean batch 1.13 / 1.76 / 5.35, peak 3 / 10 / 39
- the gate's own legs: durable.s1 5412 records over 5412 barriers (mean
1.0, peak 1 — the inline path, one barrier per statement BY DESIGN),
durable.sN 7757 over 2296 (mean 3.38, peak 28) at 2x the throughput
- peak staged 1372 B settles the no-cap decision with a number: the batch
is tiny, so the upstream mailbox bound is sufficient
- mean_batch/peak_batch are higher-is-better (the default detector would
have called bigger batches worse)
- only the batch SHAPE metrics are waived to 100%; wmix throughput and
latency keep real tolerances (15% s1, 50% sN) — a blanket waiver would
have left the entire new leg ungated
- the live assertion `mean > 1.0` on the sN leg is what catches inertness
- gate bites: sN wmix ops_sec -60% -> FAIL on exactly that metric, 1 of 86
Verified: db-bench-quick 89 checks 0 failures; baseline refreshed (86
metrics).
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
- engine: wo_idx_probe answers single-column equality from the index
hash buckets (idx_hash_key1 reproduces idx_hash bit for bit; verify
compares exactly as the slab walk did, so results identical);
composite indexes keep the walk; both executors wired (local + DB
actor RPC)
- compiler: probe_key_of_where lowers "var.col == key" on an indexed
column to DB_PROBE; all where guards still run (guard stays the
final arbiter); keys = ident/int-literal only; Float/Bytes excluded
(engine raw-eq narrower than VM float-eq)
- measured: reads 1.3k -> 1.3M ops/s, p50 600us -> 1us (~x850);
query x830; mixread 1.3k -> 89k s1, 21 -> ~1.9k sN
- gate policy moved into the driver (tolerance_for: refresh-proof);
latency floors max(4x,100us); quick mode skips poll-bound mix
floors; both tolerance classes proven to bite
- proof: test_table wo_idx_probe suite (RED first), corpus
query-index-probe 105/0, full battery green, TSan clean, two
campaigns pass the refreshed baseline
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
- bench/baseline.json: 74 metrics from the first full campaign;
tolerances tuned by a two-run repeatability check (mix* 50%,
read/query 35%, rest 15% — rationale in _config)
- gate bites: --check mode; doctored copy fails, both real runs 74/0
- headline: durable seed 4.5k/s vs ram 297k/s (23's case); reads
O(table) at ~1.5k/s; mixread 1280 vs 21 ops/s single-vs-multi
(the arc's price); msgrate 13.4M vs 2.45M (mutex-inbox number)
- arc delta recorded in story 8; findings in sample README
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
