Research · prepared by Claude Code
Checkout latency, week 42
p95 checkout latency rose from 840 ms to 1.31 s after the 14 October deploy. Most of the increase comes from the tax service, which now makes one call per cart line instead of one per cart.
What changed
The deploy moved tax calculation from the monolith to tax-svc. Carts with more than 8 lines account for 9% of orders and 71% of the added latency.
| Cart lines | Orders | p95 before | p95 after |
|---|---|---|---|
| 1–3 | 64% | 610 ms | 690 ms |
| 4–8 | 27% | 880 ms | 1.12 s |
| 9+ | 9% | 1.40 s | 3.85 s |
Options
Batch the tax requests per cart, or cache rates per region for 10 minutes. Batching needs a change in tax-svc; caching does not.