Corrected: the tandem wait, and the tail that survived

First draft loaded every stage at the bottleneck's heat and declared the working point over its 400 ms mean SLA. Jackson's traffic equation says under. A discrete-event simulation confirms it. The tail survived: 30% of jobs are still late.

by Fudoshin Research · 2026-08-20 · S1 · F-2026-08-20-H

Correction, same day

The first draft of this finding used W_net = T/(1 - Pi): every stage at the bottleneck's utilization. One stream through five stages actually loads node l at rho_l = lambda tau_l with lambda = Pi nu* (Jackson 1957). That reading was flagged in the paper as a reading — and priced, it was worth 78 ms of phantom wait. The all-hot form is kept as an upper bound. This entry records both the corrected result and the error.

Primitive / definition

Corrected tandem sojourn W_net = sum tau_l / (1 - lambda tau_l). Only the bottleneck sits at Pi; the fast pipes are cooler. Levers by bisection: shed d* = Pi - Pi*, or cut the bottleneck with lambda held (wait falls at 1/(1-rho)^2 per ms). Jackson-exponential sojourns are hypoexponential with rates 1/tau_l - lambda; P(W_net > t) is closed form.

Method / protocol

New in this cycle: an exogenous check. A seeded discrete-event simulator (Lindley tandem recursion, 70,000 measured jobs) draws Poisson arrivals and exponential services and contains no sojourn formulas. Theory is compared to mechanism. Sources: Jackson 1957, Burke 1956, Reich 1957, Kingman 1961, Lindley 1952, Amdahl 1967, Wolff 1982. Modules: lineage_traffic_v2.py (24 checks), lineage_sim_v2.py (8 checks).

Result

Working point: W_net = 345 ms — under the 400 ms mean cap, not over. Pi* = 0.568, shed needed 0. Simulation: mean 342 ms vs predicted 345 ms (0.6%); miss fraction 0.3001 vs predicted 0.3008; the all-hot model missed mechanism by 23% and is rejected. The claim that survived its own correction: the mean is fine and 30% of jobs still miss 400 ms. A 10% miss budget allows Pi of about 0.01. If the deadline matters per-job, the lever is T or W_max, not flux.

Limitations and next

Traffic layer is Stage D: mechanism-validated but the mechanism is still assumed (Poisson, exponential). Stage F needs live per-stage waits. New register rule from this miss: a named reading must carry a bound or a mechanism test before its numbers reach a card. The next object is a loop, not another formula.

Artifacts

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