How do you handle caching and invalidation in RTK Query?

RTK Query automatically handles caching by storing fetched data in its internal cache and reusing it when the same query is requested again. This helps minimize redundant network requests and improves performance.

Key Concepts in Caching and Invalidation

1
Automatic Caching: RTK Query caches query results based on the query arguments. If the same query is made again, cached data is used instead of fetching it again.
2
Cache Lifetime: You can control how long cached data remains valid using options like keepUnusedDataFor (default is 60 seconds).
3
Tag-Based Invalidation: Endpoints can provide and invalidate tags to manage cache consistency. When a mutation invalidates a tag, all queries using that tag are automatically refetched.
4
Manual Refetching: You can still manually trigger a refetch using the refetch method or by invalidating specific cache tags programmatically.

Example: Using Tags for Cache Invalidation

In the above example, whenever a new post is added using the addPost mutation, it invalidates the Posts tag. RTK Query then automatically refetches the getPosts query to keep the UI in sync with the latest data.

This tag-based system ensures efficient and predictable cache updates, while giving developers the flexibility to control when and how data should refresh.

Difficulty: 6/10

Topics: caching, invalidation, tagging

Scenario Questions

0-2 years experience

1
We need a new list view that fetches items with RTK Query. How would you set up the query to cache the results and ensure the data refreshes when the user pulls to refresh?
2
If a component using useGetUserQuery unmounts and mounts again shortly after, what does RTK Query do with the cached data, and how can you control that behavior?
3
After a user edits their profile on the same page, how would you make sure the profile query shows the updated data without a full page reload?

2-5 years experience

1
We noticed that after a user updates their settings, the settings page still shows stale data for a few seconds. Walk me through how you'd investigate and fix the caching/invalidation logic in RTK Query.
2
Our app has endpoints for a list of projects and individual project details. How would you configure cache invalidation so that updating a project via a mutation correctly updates both caches?
3
During load testing we saw the cache size grow unbounded because many query arguments are used. What strategies does RTK Query provide to limit cache size or evict entries, and how would you apply them?

5-8 years experience

1
Design a caching and invalidation strategy for a large dashboard that pulls data from several RTK Query endpoints, some of which need real‑time updates via websockets. How would you coordinate cache lifetimes and manual invalidations?
2
Explain how you would keep cache consistency when multiple users can edit the same resource concurrently, considering optimistic updates, tag‑based invalidation, and potential race conditions.
3
Our team wants to migrate from a custom caching layer to RTK Query across many micro‑frontends. What architectural considerations and pitfalls would you watch for regarding cache invalidation across module boundaries?

8+ years experience

1
At the organization level we plan to standardize caching policies across all React apps using RTK Query. How would you define a shared invalidation strategy, tag conventions, and tooling to enforce consistency across teams?
2
Discuss the trade‑offs of relying on RTK Query’s automatic cache eviction versus implementing a custom LRU cache for high‑traffic data. When might you choose one over the other, and how would you measure impact?
3
If we need to support offline‑first behavior with background sync, how would you extend RTK Query’s caching and invalidation mechanisms to reconcile server and client state after reconnection?

Follow-up Questions

❓What are the pros and cons of using short versus long `keepUnusedDataFor` values?
❓How would you verify that your invalidation tags are correctly wired in a large codebase?
❓Can you describe a situation where you’d need to manually trigger a refetch instead of relying on tags?