External API Slow

1// Volume floor pairs p75 with call_count so a single 5s cron/day doesn't fire the gate.
2const MIN_CALL_COUNT = 500;
3
4export const metadata = {
5  id: 'external_api_slow',
6  threshold: `p75Ms > 2000 AND callCount >= ${MIN_CALL_COUNT}`,
7  billingDimension: 'function-duration',
8  scope: 'route',
9  sourceCitation: 'vercel-optimize gate threshold',
10  description:
11    'External API hostnames with p75 latency above 2 seconds AND at least 500 calls in the window. External API latency is a primary driver of function duration cost when the upstream is on a hot path; a single slow stale call isn\'t worth recommending against.',
12};
13
14export function gate(signals) {
15  const apis = extractExternalApis(signals);
16  const calls = extractCallCounts(signals);
17  return apis
18    .map((a) => ({ ...a, callCount: calls.get(a.hostname) ?? 0 }))
19    .filter((a) => a.p75Ms > 2000 && a.callCount >= MIN_CALL_COUNT)
20    .map((a) => ({
21      kind: metadata.id,
22      scope: 'route',
23      route: null,
24      files: [],
25      hostname: a.hostname,
26      // Weight by latency × call volume so 100k-call/2.1s outranks 1k-call/8s.
27      priority: Math.round((a.p75Ms * a.callCount) / 1000),
28      confidence: 0.88,
29      o11ySignal: `host=${a.hostname},p75=${a.p75Ms}ms,calls=${a.callCount}`,
30      reason: 'slow external dependency on hot path',
31      question: `Which routes call ${a.hostname} (p75=${a.p75Ms}ms across ${a.callCount} calls), and can the call be parallelized, cached, or moved off the critical path?`,
32      evidence: { metric: 'externalApiP75', hostname: a.hostname, p75Ms: a.p75Ms, callCount: a.callCount },
33    }));
34}
35
36function extractExternalApis(signals) {
37  const m = signals.metrics?.externalApiP75;
38  if (!m?.ok && !Array.isArray(m?.rows)) return [];
39  return (m?.rows ?? [])
40    .map((r) => ({
41      hostname: r.origin_hostname,
42      p75Ms: Math.round(r.value ?? 0),
43    }))
44    .filter((a) => a.hostname);
45}
46
47function extractCallCounts(signals) {
48  const m = signals.metrics?.externalApiCount;
49  const out = new Map();
50  if (!m) return out;
51  for (const r of m.rows ?? []) {
52    if (r?.origin_hostname) out.set(r.origin_hostname, r.value ?? 0);
53  }
54  return out;
55}