# Cache invalidation storm: pre-release checklist

Source: https://releasefailures.com/incidents/cache-invalidation-storm/
Content version: 1.0.0
Verified on: 2026-10-21
Licence: CC BY 4.0

Definition: A deploy flushes or invalidates caches at once and origin load spikes.
- [ ] PR-01 Add a unit test that runs the changed settings cache write path against existing entries and asserts their expiry times do not change. (test class: Unit tests)
- [ ] PR-02 Add a unit test that asserts the killswitch for the caching mechanism restores the previous write path when switched off. (test class: Unit tests)
- [ ] PR-03 Expire all user settings cache entries in a production-shaped environment and measure replication delay on dependent services during the rewrite, and fail when replication delay exceeds the dependent services' timeout. (test class: Load and performance tests)
- [ ] PR-04 Run each cache-fronted scatter query at stepped cache miss rates up to 100 percent and record read load on every shard at each step, and fail when any shard exceeds its read capacity. (test class: Load and performance tests)
- [ ] PR-05 Confirm the database behind the channel membership cache serves full-miss read load from replicas within its query timeout. (test class: Load and performance tests)
- [ ] PR-06 Restart the service discovery agent on a share of cache hosts in staging and confirm those cache nodes are neither replaced with empty nodes nor flushed. (test class: Chaos and resilience tests)
- [ ] PR-07 Throttle client boot requests in a drill and confirm the limit can be raised in steps as the cache refills. (test class: Chaos and resilience tests)