[PR #498] [MERGED] fix: dedup stale background refetches in fetch cache #620

New issue

Closed

opened 2026-05-06 13:09:07 +02:00 by BreizhHardware · 0 comments

BreizhHardware commented

2026-05-06 13:09:07 +02:00

Owner

📋 Pull Request Information

Original PR: https://github.com/cloudflare/vinext/pull/498
Author: @NathanDrake2406
Created: 3/12/2026
Status: ✅ Merged
Merged: 3/12/2026
Merged by: @james-elicx

Base: main ← Head: fix/fetch-cache-stale-dedup

📝 Commits (7)

d4be71d fix: dedup stale background refetches in fetch cache
f6d0063 test: add fetch cache stale dedup concurrency tests
e57c05e Update packages/vinext/src/shims/fetch-cache.ts
2faabaa fix: repair broken setTimeout structure from review suggestion
8c7baaf fix: wrap fake timer tests in try/finally for safety
5caf79e fix: guard background revalidation against caching error responses
b4840c0 fix: tighten cache guard to status === 200

📊 Changes

2 files changed (+423 additions, -39 deletions)

View changed files

📝 packages/vinext/src/shims/fetch-cache.ts (+94 -37)
📝 tests/fetch-cache.test.ts (+329 -2)

📄 Description

Summary

Every concurrent request hitting a stale fetch cache entry was independently calling originalFetch(), creating a thundering herd on popular endpoints
Added a per-cache-key dedup map (pendingRefetches) shared across RSC/SSR environments via Symbol.for(), matching the existing ISR regeneration dedup pattern in isr-cache.ts
Added a 60s timeout safety net that force-cleans dedup entries when upstream fetches hang, with identity checks in both .finally() and setTimeout to prevent slot-ownership races
Improved error log to include URL and truncated cache key for production observability

Test plan

Concurrent stale hits trigger only one background refetch (deferred promise gate ensures deterministic timing)
Completed refetches allow new ones (lifecycle test)
Failed refetches clean up dedup entry, allowing retry (error-path test)
Hung fetches are force-cleaned after 60s timeout (vi.useFakeTimers)
Late-settling hung fetch does not evict a replacement refetch's slot (race test)
_resetPendingRefetches() called in beforeEach for test isolation
CI: full Vitest suite + Playwright E2E

_{🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.}

## 📋 Pull Request Information **Original PR:** https://github.com/cloudflare/vinext/pull/498 **Author:** [@NathanDrake2406](https://github.com/NathanDrake2406) **Created:** 3/12/2026 **Status:** ✅ Merged **Merged:** 3/12/2026 **Merged by:** [@james-elicx](https://github.com/james-elicx) **Base:** `main` ← **Head:** `fix/fetch-cache-stale-dedup` --- ### 📝 Commits (7) - [`d4be71d`](https://github.com/cloudflare/vinext/commit/d4be71d1a34501f6caf226592111857ed39faff2) fix: dedup stale background refetches in fetch cache - [`f6d0063`](https://github.com/cloudflare/vinext/commit/f6d006340ec18e29f5b4e4f9511b74ae86a97244) test: add fetch cache stale dedup concurrency tests - [`e57c05e`](https://github.com/cloudflare/vinext/commit/e57c05e51085c7c81f53ce1f43de5da8a1f15834) Update packages/vinext/src/shims/fetch-cache.ts - [`2faabaa`](https://github.com/cloudflare/vinext/commit/2faabaa6639368681ba85b6b7bd1ba37c77e8fe7) fix: repair broken setTimeout structure from review suggestion - [`8c7baaf`](https://github.com/cloudflare/vinext/commit/8c7baaf6929412dc27ba2b8b8ad9bda56b55f21b) fix: wrap fake timer tests in try/finally for safety - [`5caf79e`](https://github.com/cloudflare/vinext/commit/5caf79ee62e94fb11b4ed15256b2e90161f5f571) fix: guard background revalidation against caching error responses - [`b4840c0`](https://github.com/cloudflare/vinext/commit/b4840c00f152e245942e4ed9373bce80ff6627d8) fix: tighten cache guard to status === 200 ### 📊 Changes **2 files changed** (+423 additions, -39 deletions) <details> <summary>View changed files</summary> 📝 `packages/vinext/src/shims/fetch-cache.ts` (+94 -37) 📝 `tests/fetch-cache.test.ts` (+329 -2) </details> ### 📄 Description ## Summary - Every concurrent request hitting a stale fetch cache entry was independently calling `originalFetch()`, creating a thundering herd on popular endpoints - Added a per-cache-key dedup map (`pendingRefetches`) shared across RSC/SSR environments via `Symbol.for()`, matching the existing ISR regeneration dedup pattern in `isr-cache.ts` - Added a 60s timeout safety net that force-cleans dedup entries when upstream fetches hang, with identity checks in both `.finally()` and `setTimeout` to prevent slot-ownership races - Improved error log to include URL and truncated cache key for production observability ## Test plan - [x] Concurrent stale hits trigger only one background refetch (deferred promise gate ensures deterministic timing) - [x] Completed refetches allow new ones (lifecycle test) - [x] Failed refetches clean up dedup entry, allowing retry (error-path test) - [x] Hung fetches are force-cleaned after 60s timeout (`vi.useFakeTimers`) - [x] Late-settling hung fetch does not evict a replacement refetch's slot (race test) - [x] `_resetPendingRefetches()` called in `beforeEach` for test isolation - [ ] CI: full Vitest suite + Playwright E2E --- <sub>🔄 This issue represents a GitHub Pull Request. It cannot be merged through Gitea due to API limitations.</sub>