Conventions Perf

Performance Guard Conventions

Apply when a performance-guard check fails in CI, or when touching a route or endpoint flagged by the live bun scripts/perf-hotspots.ts report.

Overview

Stella guards performance with recorded budgets, diffed on every run. A regression either fails CI outright or shows up as a reviewable diff in the PR. Six guards exist today:

• Network baseline (apps/web/e2e/network-baseline.json, checked by apps/web/e2e/helpers/network.ts from apps/web/e2e/specs/route-smoke.spec.ts): per-route request manifest, waterfall depth, per-request repeat budget, and per-request DB query budget.
• Bundle baseline (scripts/bundle-baseline.ts + scripts/bundle-baseline.json): gzipped size per vendor/entry/route chunk group, wired into the web-build CI job via --check.
• React Compiler bailout guard (scripts/rc-bailouts.ts + scripts/react-compiler-bailouts.json): tracks every component the compiler cannot memoize, so a bailout losing its manual useMemo/useCallback fails CI instead of silently reintroducing an infinite-update-loop risk.
• DB query counter (apps/api/src/lib/db-query-counter.ts): the runtime half of the network baseline's DB-query budget. Dev/test only.
• require-loader-prefetch oxlint rule (.oxlint-plugins/require-loader-prefetch.ts): static, not baseline-based; flags the waterfall pattern the network baseline would otherwise only catch after the fact.
• Per-iteration I/O checks: scripts/db-await-in-loop.ts (type-aware, CI) flags a database call awaited once per loop iteration (the N+1), recognizing handles by type rather than name and suppressed with // db-await-in-loop: <reason>. A single DB hit in a constant-sized batch round (canonical chunked or an array slice-step loop, size >= 2), a fixed set of at most 16 elements, or a nonnegative constant-start counter (constant bound <= 16) is accepted when no enclosing loop or fan-out exists. Multiple hits, nested per-row work, variable sizes, mutated counters and keyset walks still require batching or an explicit reason. no-network-await-in-loop flags an HTTP request, AWS SDK command dispatch, or API-client method awaited the same way (iterations x RTT). Both are static and both name the owner, so the fix is concrete: batch the calls, or record in the suppression reason why the sequence is required. There is no generic await-in-loop rule; a sequential await with no I/O behind it costs nothing to guard.

The Core Norm

Fix the regression first. A red guard means the change made something slower, heavier, or chattier than before. Reseeding the baseline to make CI green is not a mechanical step; it is a product decision that the regression is acceptable, and it must be justified in the PR description (why the extra request, the deeper wait, or the bigger chunk is worth it).

Main owns network recordings. The main-only recorder runs after route/runtime merges and nightly; the delivery workflow validates and publishes a baseline artifact keyed by the recorded commit. PR and merge-queue checks load the newest published recording at or before their merge base (or the committed file at that same base when recording is unavailable). They never edit the shared JSON or request a baseline:record delivery.

New and removed routes are scoped from changed route sources and reported in the job summary. Existing routes retain every allowance, including routes whose source changed. An intentional increase requires a reviewed JSON file in apps/web/e2e/network-budgets/<change>.json with route, a nonempty reason, and a complete budget entry (depth, requests, and applicable requestCounts, dbQueries, responseSizes). Only declarations added or modified since the merge base apply; inherited declarations cannot repeatedly widen future checks. Use one file per change, so unrelated changes do not share a generated baseline conflict.

E2E_NETWORK_BASELINE=write and rewrite remain local measurement modes; main recording defaults to write; dispatch with mode=rewrite after a performance fix to tighten it. Do not commit measurement output on a PR.

The bundle baseline mirrors this with --write-baseline (regenerate) and a RATCHET_DOWN prompt (not a failure) when a chunk shrinks by more than 3%, so a real win gets locked in rather than silently drifting back up. The RC bailout guard and the query counter follow the same "commit the smaller number, don't just silence the check" norm.

Failure Playbook

New request on route

network.ts reports New API request(s) on <route>. The route now calls an endpoint it did not before. If intentional, declare the reviewed budget. If not, find what changed (a new hook mount, a widened select, an added useQuery) and remove the call.

Request waterfall got deeper

Request waterfall got deeper on <route>: N -> M. Each extra level is one more sequential network round the user waits through. The fix is almost always to start the query in the route loader instead of the component: prefetch it with ensureRouteQueryData (blocking, critical data) or prefetchRouteQuery (non-blocking warmup) from apps/web/src/lib/react-query.ts, so the fetch starts during navigation in parallel with code-split chunk loading, and the component's useSuspenseQuery consumes an already-warm cache instead of opening a new round. require-loader-prefetch catches the same pattern statically before it ever reaches the baseline: it flags useSuspenseQuery(factory(...)) when the route has no loader, or has one that never references factory.

Request repeated more than budgeted

API request repeated on <route>: <key> ran N -> M times. Baseline budgets per-request-key repeat counts (default 1 unless the committed requestCounts says otherwise). Duplicate firing usually comes from duplicate component mounts, normalized UUID fan-out (multiple ids hitting the same :id-normalized key), or a refetch policy that lets the same endpoint fire twice. Reuse the in-flight query instead of issuing a second one.

DB query count grew

DB queries per request grew on <route>: <key> ran N -> M queries. The classic cause is an N+1: a per-row query inside a loop, or a lazy relation loaded once per item instead of preloaded. Batch it (joins, IN lists, Drizzle relation preloading); see /conventions-db for indexing and batching patterns. The allowance (dbQueryAllowance, budget + max(2, 15%)) already absorbs normal noise (auth session-refresh piggybacks, cache variance); a failure here is a real regression, not jitter.

If instead the check reports DB query count missing on <route>, the response stopped exposing the dev/test x-db-queries header — restore the query counter wiring before trusting the route's N+1 budget again.