Essential Caching Concepts: Fundamentals Quiz Quiz

Test your knowledge of caching basics, including cache keys, TTL, cache types, and invalidation strategies. Ideal for beginners seeking a clear understanding of cache management, expiration policies, and best practices.

1. Cache Key Uniqueness

   Which factor is most important when creating a cache key for storing user-specific data?

   1. Making all keys the same for simpler lookup
   2. Using only the current date
   3. Excluding any user information
   4. Including a unique user identifier in the key

   Explanation: A cache key should uniquely identify the data it stores, so including a unique user identifier ensures each user's data is kept separate and correctly retrievable. Using only the current date or making all keys the same would create conflicts and overwrite data. Excluding user information means different users cannot be distinguished, which defeats personalized caching.

2. Understanding TTL in Caching

   In the context of caching, what does the term 'TTL' stand for and control?

   1. Token Transfer Length; it limits the key size
   2. Transaction Time Log; it tracks request durations
   3. Total Traffic Limit; it sets a cap on cache requests
   4. Time to Live; it determines how long an item remains in the cache

   Explanation: TTL stands for 'Time to Live' and defines the duration an item should stay in the cache before it expires and is removed. Total Traffic Limit does not relate to cache expiration, Token Transfer Length is not a caching term, and Transaction Time Log is not connected to cache lifespan or eviction.

3. Client vs Server Cache Differences

   Which statement best describes the main difference between client-side and server-side caching?

   1. Client-side cache cannot store any images or files
   2. Client-side cache stores data locally for individual users, whereas server-side cache holds data centrally for multiple users
   3. Server-side cache is always faster than client cache
   4. Server-side cache is less secure than client cache

   Explanation: Client-side caches operate on the user's device and are personalized, while server-side caches store data on servers accessible to multiple clients. While speed and security can vary depending on implementation, there's no rule that server cache is always faster or less secure. Client caches can also store images and files.

4. Cache Invalidation Basics

   Why is cache invalidation important in web applications that frequently update their data?

   1. It ensures users see the most up-to-date information when data changes
   2. It prevents data from ever being updated
   3. It increases cache size indefinitely
   4. It reduces the original data source to zero usage

   Explanation: Cache invalidation is necessary so users don't receive outdated responses after the underlying data changes. Increasing cache size indefinitely would waste resources, not solve freshness. Preventing data updates has the opposite effect. While effective caching reduces data source load, invalidation doesn't reduce usage to zero.

5. Examples of Cache Expiration

   If a cached news article has a TTL of 10 minutes, what happens when a user requests it 15 minutes after caching?

   1. The article is deleted from the entire system
   2. The cache automatically doubles its TTL
   3. The cache is bypassed and fresh data is fetched
   4. The expired version is shown without warnings

   Explanation: Once TTL expires, the cache is no longer valid, so the system fetches the latest data from the source. Showing an expired version would deliver stale information. Deleting the article entirely is not typical, and caches do not automatically increase their TTL.

6. Cache Key Collisions

   What is a potential problem if two different pieces of data share the same cache key?

   1. It improves performance by reducing the number of keys
   2. It increases security by hiding data identities
   3. It allows unlimited cache growth
   4. One data item may overwrite the other, leading to incorrect information

   Explanation: When two different data items use the same cache key, one can overwrite the other, causing users to receive the wrong information. While fewer keys might seem efficient, it sacrifices correctness. Key collisions do not improve security, nor do they contribute to unlimited cache capacity.

7. Setting Appropriate Cache TTLs

   Which cache TTL would be most appropriate for frequently-updated stock prices?

   1. No TTL, keep data forever
   2. A long TTL, like several days
   3. A short TTL, like a few seconds
   4. Randomly changing TTL values

   Explanation: Stock prices change rapidly, so a short TTL ensures users receive fresh information with minimal delay. A long TTL would cause outdated data to be shown. Keeping data forever means never updating, which is unsuitable for volatile information. Random TTL values provide no consistency or reliability.

8. Purpose of Cache Invalidation Strategies

   Which cache invalidation strategy involves removing or updating cache entries when the original data changes?

   1. No-cache policy
   2. Write-through
   3. Over-caching
   4. Static cache

   Explanation: Write-through strategies update or invalidate cache entries immediately when the underlying data changes, maintaining consistency. A no-cache policy does not store any data to cache. Static cache does not address updates, and over-caching is an undesirable scenario where excessive data is cached without management.

9. Client-Side Cache Example

   Which scenario is an example of client-side caching in a web application?

   1. A database holds query results in memory for all clients
   2. A user's browser keeps a copy of a visited image for quick reloading
   3. Backend services coordinate shared data in memory
   4. A central server delivers pre-rendered web pages to all users

   Explanation: Client-side caching happens when the user's device, such as a browser, retains data locally for faster access. Server-side or backend services focus on central and shared caching, while database caching is a server process. Only the browser scenario genuinely represents client-side caching.

10. Downside of Overly Aggressive Caching

    What is a main risk of using overly aggressive caching policies?

    1. It prevents any data from being deleted
    2. Cache memory is instantly doubled
    3. Users may receive outdated or incorrect data
    4. All cache keys become identical

    Explanation: Aggressive caching prioritizes speed at the expense of freshness, meaning users might see stale or wrong data if the cache is not refreshed frequently enough. Making all cache keys the same would cause data collisions, not necessarily bad freshness. Cache memory doesn't automatically double, and aggressive caching often leads to unnecessary retention, not prevention of deletions.