Cache invalidation strategies in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is cache invalidation in system design?

Cache invalidation is the process of removing or updating cached data when the original data changes, ensuring that users get fresh and accurate information.

beginner

Explain the 'Time-to-Live (TTL)' cache invalidation strategy.

TTL sets a fixed time duration for cached data. After this time expires, the cache entry is automatically removed or refreshed, ensuring data does not become too old.

intermediate

What is the difference between 'Write-through' and 'Write-back' cache invalidation?

Write-through updates the cache and the main data store simultaneously, keeping them in sync. Write-back updates only the cache first and writes to the main store later, which can cause stale data if not managed carefully.

intermediate

Describe the 'Explicit Invalidation' strategy.

Explicit invalidation means the system actively removes or updates cache entries when data changes, often triggered by events or notifications, ensuring immediate consistency.

advanced

Why is cache invalidation considered one of the hardest problems in computer science?

Because it requires balancing data freshness, system performance, and complexity. Incorrect invalidation can lead to stale data or excessive overhead, making it tricky to design efficient and reliable systems.

Which cache invalidation strategy removes cache entries after a fixed time?

A Write-back

B Explicit Invalidation

C Time-to-Live (TTL)

D Lazy Loading

TTL sets a fixed expiration time for cache entries, after which they are invalidated.

In which strategy is the cache updated immediately along with the main data store?

A Write-back

B Write-through

C Lazy Invalidation

D TTL

Write-through updates both cache and main store at the same time to keep data consistent.

What is a risk of using write-back cache invalidation?

A Stale data if main store update is delayed

B Automatic cache refresh

C Cache entries never expire

D Cache and main store always in sync

Write-back delays main store update, which can cause stale data if not handled properly.

Which strategy requires the system to actively remove cache entries when data changes?

A Lazy Loading

B TTL

C Write-back

D Explicit Invalidation

Explicit invalidation means actively removing or updating cache entries on data change.

Why is cache invalidation challenging in system design?

A Because it balances freshness, performance, and complexity

B Because it never affects system performance

C Because cache is always fresh

D Because it only applies to databases

Cache invalidation is hard because it must balance data freshness, system speed, and design complexity.

Explain the main cache invalidation strategies and when to use each.

Think about how and when cached data gets updated or removed.

Describe why cache invalidation is important and what problems it solves in system design.

Consider what happens if cache is not updated properly.