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fix: eliminate cache stampede across all server handlers #378

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fix: eliminate cache stampede across all server handlers #378

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80 changes: 44 additions & 36 deletions server/worldmonitor/military/v1/get-theater-posture.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ import type {
TheaterPosture,
} from '../../../../src/generated/server/worldmonitor/military/v1/service_server';

import { getCachedJson, setCachedJson } from '../../../_shared/redis';
import { getCachedJson, setCachedJson, cachedFetchJson } from '../../../_shared/redis';
import {
isMilitaryCallsign,
isMilitaryHex,
Expand Down Expand Up @@ -183,43 +183,51 @@ function calculatePostures(flights: RawFlight[]): TheaterPosture[] {
// RPC handler
// ========================================================================

async function fetchTheaterPostureFresh(): Promise<GetTheaterPostureResponse> {
// Race both sources in parallel instead of sequential fallback (H-6 fix)
let flights: RawFlight[];
const [openskyResult, wingbitsResult] = await Promise.allSettled([
fetchMilitaryFlightsFromOpenSky(),
fetchMilitaryFlightsFromWingbits(),
]);

if (openskyResult.status === 'fulfilled' && openskyResult.value.length > 0) {
flights = openskyResult.value;
} else if (wingbitsResult.status === 'fulfilled' && wingbitsResult.value && wingbitsResult.value.length > 0) {
flights = wingbitsResult.value;
} else {
throw new Error('Both OpenSky and Wingbits unavailable');
}

const theaters = calculatePostures(flights);
const result: GetTheaterPostureResponse = { theaters };

// Write stale/backup tiers in background
Promise.all([
setCachedJson(STALE_CACHE_KEY, result, STALE_TTL),
setCachedJson(BACKUP_CACHE_KEY, result, BACKUP_TTL),
]).catch(() => {});

return result;
}

export async function getTheaterPosture(
_ctx: ServerContext,
_req: GetTheaterPostureRequest,
): Promise<GetTheaterPostureResponse> {
const cached = (await getCachedJson(CACHE_KEY)) as GetTheaterPostureResponse | null;
if (cached) return cached;

try {
// Race both sources in parallel instead of sequential fallback (H-6 fix)
let flights: RawFlight[];
const [openskyResult, wingbitsResult] = await Promise.allSettled([
fetchMilitaryFlightsFromOpenSky(),
fetchMilitaryFlightsFromWingbits(),
]);

if (openskyResult.status === 'fulfilled' && openskyResult.value.length > 0) {
flights = openskyResult.value;
} else if (wingbitsResult.status === 'fulfilled' && wingbitsResult.value && wingbitsResult.value.length > 0) {
flights = wingbitsResult.value;
} else {
throw new Error('Both OpenSky and Wingbits unavailable');
}

const theaters = calculatePostures(flights);
const result: GetTheaterPostureResponse = { theaters };

await Promise.all([
setCachedJson(CACHE_KEY, result, CACHE_TTL),
setCachedJson(STALE_CACHE_KEY, result, STALE_TTL),
setCachedJson(BACKUP_CACHE_KEY, result, BACKUP_TTL),
]);
return result;
} catch {
const stale = (await getCachedJson(STALE_CACHE_KEY)) as GetTheaterPostureResponse | null;
if (stale) return stale;
const backup = (await getCachedJson(BACKUP_CACHE_KEY)) as GetTheaterPostureResponse | null;
if (backup) return backup;
return { theaters: [] };
}
// cachedFetchJson coalesces concurrent requests — only one upstream fetch
// runs at a time, eliminating the stampede that was hammering Wingbits.
const result = await cachedFetchJson<GetTheaterPostureResponse>(
CACHE_KEY,
CACHE_TTL,
fetchTheaterPostureFresh,
);
if (result) return result;

// Upstream failed and nothing was cached — fall back to stale/backup tiers
const stale = (await getCachedJson(STALE_CACHE_KEY)) as GetTheaterPostureResponse | null;
if (stale) return stale;
const backup = (await getCachedJson(BACKUP_CACHE_KEY)) as GetTheaterPostureResponse | null;
if (backup) return backup;
return { theaters: [] };
}