Troubleshooting

Common Issues

Cache Not Updating (Zombies)

If you find that your cache isn't updating after a mutation, check the following:

1. Epoch Mismatch: Ensure you are invalidating the correct route pattern.
2. Success Status: Invalidation only triggers on 2xx responses. If your POST/PUT fails, the cache won't be invalidated.
3. Race Conditions: SWR can sometimes serve stale data if a refresh is still pending.

High Memory Usage

If your Node.js process is consuming too much memory:

1. Reduce maxBodySize: Prevent large responses from being buffered.
2. Shorten gcTime: Evict stale data more aggressively.
3. Use Redis: Offload the cache storage from your Node.js heap to an external Redis instance.

Unexpected MISS on GET requests

1. Vary Headers: If you use vary, any change in those headers will cause a MISS.
2. Query Params: If sortQuery is false, ?a=1&b=2 and ?b=2&a=1 are treated as different routes.

Debugging

You can inspect the X-Cache header in your browser's network tab or via curl:

curl -I http://localhost:3000/api/data

Look for:

• X-Cache: HIT (Serving from cache)
• X-Cache: MISS (Fetched from source)
• X-Cache: STALE (Serving stale, refreshing in background)