The max/median ratio inverts the actual user-facing p90 ranking:
sticky: hotspot=2.73 but system e2e p90 = 34.6s (worst)
unified: hotspot=3.67 but system e2e p90 = 18.0s (best)
because sticky's median is also high (everyone slow) while unified
concentrates the damage on one worker and keeps the other 7 fast.
Any "imbalance" metric structurally punishes the affinity-then-escape
schemes that we actually want to advocate for.
Changes:
- analysis/characterization/render_window1_figures.py:
fig_b3_per_worker_ttft now annotates each subplot with
"median X.Xs · max Y.Ys" instead of "hotspot=Y.YY"; docstring
documents why we drop the ratio.
- figs/f4c_per_worker_ttft.png: regenerated with new titles.
- figs/f4c_apc_vs_hotspot_tradeoff.png: deleted. The scatter's y-axis
was the deprecated ratio; superseded by f4c per-worker bars + f6
e2e bars which together carry the same information honestly.
- PAPER_OUTLINE.md: C3, §3.3, §4.1 wording, §5 metric list, §8
conclusion — replace "hotspot index" mentions with
"worst-worker p90" or "(median, max) worker p90"; promote the
§3.3 methodology note to a top-level sub-finding ("hot pin
failure must be measured with per-worker absolute latency,
not normalized ratio").
- MEETING.md: §3.3 narrative reworded to lead with the (median, max)
pair directly; explicit one-line note on why the ratio is dropped.
Conceptual uses of "hot session" / "hot instance" / "hot pin" remain
unchanged — only the *metric* called hotspot index is retired.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
'capped' is not a routing policy — it's lmetric run on a separately
truncated trace (sessions capped to 8 turns via build_capped_trace.py).
Putting it alongside lmetric/load_only/sticky/unified in per-policy
comparison figures is misleading because the workload differs, not
the routing decision. Comparing apples to a different-trace orange
inflates/deflates apparent policy gaps for the wrong reasons.
Regenerated 4 figures with --exclude-policies capped on
analysis/characterization/render_window1_figures.py:
- f4a_apc_loss.png (APC bars)
- f4c_apc_vs_hotspot_tradeoff.png (APC vs hotspot scatter)
- f4c_per_worker_ttft.png (per-worker TTFT panel)
- f6_e2e_latency_bars.png (TTFT/TPOT/E2E bars)
Added --exclude-policies CLI flag to the renderer so this is a
reversible choice, not a permanent script mutation. capped data remains
in b3_policy_comparison.json and can be brought back in workload-
sensitivity sections (where it actually belongs) by omitting the flag.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
User pointed out the apparent paradox: in fig_b3_per_worker_ttft_p90, unified
has hotspot index 3.67 while sticky has 2.73, yet unified e2e p90 is roughly
half of sticky's. Resolution: hotspot index (max/median) is a *ratio* and
misleading on its own. Per-worker absolute TTFT p90:
sticky : median 20.3s, max 55.4s -> system e2e p90 34.6s
unified: median 10.3s, max 37.7s -> system e2e p90 18.0s
Mechanism: top 1% sessions own 46.5% input mass and there are more hot
sessions than instances (8), so sticky's hash binding gives *every* worker
its own hot session and the median worker is also slow. Unified's LMetric
fallback re-routes cold/new sessions away from hot affinity instances,
preserving 7/8 worker speed. System p90 is dominated by the majority of
requests landing on fast workers, hence the 2x e2e gap.
Changes:
- Replace §3.3 figure with figs/f4c_per_worker_ttft.png (per-worker bars)
instead of figs/f4c_apc_vs_hotspot_tradeoff.png (the ratio scatter)
- §3.3 narrative in PAPER_OUTLINE.md and MEETING.md rewritten around
absolute median + max + system e2e p90 instead of hotspot ratio
- Add a §3.3 sub-finding: "hot pin failure must be measured with
per-worker absolute latency, not normalized ratio"
- Keep the scatter as supplementary for §5 multi-policy summary
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
