- `randread N R` in the sample: fill N rows, read R across the WHOLE range
- Weyl order `i*2654435761 mod n` — no RNG in the language, none needed;
both legs read the SAME key order so residency is the only variable
- `randread` driver leg: control (256 MiB, does not bind) vs over-cap
(6 MiB + swap), sizes kept modest — quick resolves it in ~5s
- gates the RATIO, not the absolutes: over-cap reads/sec belongs to the
box's swap device, the factor between two runs belongs to the engine
- reads must all resolve (hits == R) or the leg fails; a collapse measured
over unresolved reads is noise
- 133 checks, 0 failures; gate bites on a doctored collapse_x
Measured — this closes the gap the swap leg left:
- resident 1 851 166 reads/sec, p50 0us p99 1us
- over-cap 6 771 reads/sec, p50 128us p99 487us
- 273x throughput, ~480x p99, all 20 000 reads resolving in both
- so the two access patterns sit ~270x apart under identical pressure:
append-mostly insert ~1%, random read 273x
- departure is a STEP not a curve (1us -> 487us, nothing between), which
is why p99_departure_decile finds no knee — there is none
- caveat recorded, NOT inherited: this is demand-paged anonymous memory
through swap (4 KiB/fault, no readahead). `resident: keys` preads via
the page cache — should be better, but databasev2 2 task 7 must measure
its own read path. New criterion added there
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
shoney.arickathil
a873cf7331