Fundamentals of Caching: Keys, TTL, and Client-Server Concepts Quiz

Test your knowledge of basic caching concepts including cache keys, time-to-live (TTL) settings, and client-server interactions. This quiz covers core caching terminology and scenarios to help you assess your understanding of efficient data storage and retrieval.

1. TTL Definition

   What does TTL (Time To Live) specify in the context of caching?

   1. The name of the server managing the cache
   2. The total storage capacity of the cache
   3. The number of users allowed to access the cache
   4. The maximum time a cached item remains valid before expiring

   Explanation: TTL, or Time To Live, defines how long a piece of data should stay in the cache before it is considered stale and removed. It helps ensure cache accuracy and freshness. The number of users or total storage capacity are unrelated to TTL, and the server’s name does not define caching lifespans. These distractors confuse TTL with other configuration settings.

2. Cache Key Purpose

   Which best describes a cache key's purpose in a cache system?

   1. To restrict access to the cache server
   2. To measure the size of cached data
   3. To uniquely identify and retrieve a specific cached value
   4. To encrypt client requests

   Explanation: A cache key acts as a unique identifier for storing and fetching data in the cache. It enables fast lookups by mapping requests to their cached responses. Restricting access, measuring size, or encrypting requests are important functions but unrelated to the core purpose of cache keys.

3. Client Caching

   When a client caches a response locally, what is one potential benefit?

   1. Increased server bandwidth usage
   2. Higher data transfer costs
   3. Faster subsequent data retrieval for the same request
   4. Longer response times for repeated requests

   Explanation: Local client caching means that future requests for the same resources can be served immediately, leading to faster response times. This process reduces, not increases, server bandwidth and data transfer costs. Longer response times are a disadvantage of not using caching.

4. Cache Expiry

   If cached data has expired due to its TTL ending, what happens on the next data request?

   1. The server automatically doubles the TTL
   2. The old data is permanently locked in the cache
   3. The data is re-fetched from the original source
   4. The client receives an error message

   Explanation: When cached data expires, the cache system fetches new data from the original source to refresh the cache. Data is not locked in the cache, and the client should not receive an error purely because data expired. TTL values are not automatically doubled; such behavior would not maintain freshness.

5. Cache Key Design

   Why is it important for cache keys to be unique for different requests?

   1. To prevent clients from connecting to the server
   2. To reduce the need for a cache
   3. To prevent returning incorrect data to users
   4. To store passwords securely

   Explanation: Unique cache keys ensure each piece of data maps only to its corresponding request, preventing accidental delivery of unrelated or incorrect cached data. Unique keys do not reduce necessity for caching, store passwords, or manage client connectivity.

6. Server vs Client Cache

   Which statement best distinguishes server-side caching from client-side caching?

   1. Client-side caching requires server access at every request
   2. Client-side caching uses more bandwidth than server-side caching
   3. Server-side caching stores data on the server; client-side caching stores data on the client device
   4. Server-side caching slows down response times

   Explanation: Server-side caching keeps data for many users on the server, while client-side caching allows individual devices to store their responses locally. The other options confuse the effects: client-side caching actually saves bandwidth and does not force server access, and server-side caching usually improves, not slows, responses.

7. Setting TTL

   Why might you choose a short TTL for frequently changing data in your cache?

   1. To allow cached data to accumulate for months
   2. To increase the chance of serving outdated data
   3. To make the cache key easier to guess
   4. To ensure users receive fresh and up-to-date information

   Explanation: A short TTL balances the benefits of caching with data freshness, updating the cache before the data becomes outdated. Long TTLs mean data could be stale; accumulating cache for months is usually undesirable for changing data. The length of TTL does not relate to security of cache keys.

8. Cache Invalidation

   What does cache invalidation mean?

   1. Splitting cache storage across multiple servers
   2. Converting values to different data types
   3. Removing or marking cached data as outdated
   4. Encrypting cache keys before use

   Explanation: Cache invalidation is the process of ensuring the cache no longer serves stale or outdated entries, either by deleting or updating them. Encrypting keys or changing data types relates to security or data structure, and splitting storage is about scaling, not invalidation.

9. When Caching Fails

   If a requested item cannot be found in the cache, what is this scenario called?

   1. Key overflow
   2. Cache miss
   3. Cache hit
   4. Time-to-leave

   Explanation: A cache miss happens when the requested data is absent from the cache, so the system fetches it from the original data source. A cache hit is the opposite, where the item is found instantly. Key overflow is not a standard caching term, and 'time-to-leave' is unrelated.

10. Cache Hits

    What occurs during a 'cache hit'?

    1. Server restarts and clears all stored data
    2. Requested data is found in the cache and returned quickly
    3. The cache key is invalid and rejected
    4. Cache is completely empty and no data can be retrieved

    Explanation: A cache hit means the needed data was already stored, so it is returned immediately for efficiency. An empty cache or server restart are not definitions of a hit. An invalid cache key may cause a miss, not a hit.

11. Cache Key Collision

    What is a cache key collision, and why is it problematic?

    1. TTL is set to an invalid value
    2. A client encrypts data before storing it
    3. Two different requests generate the same cache key, causing data confusion
    4. The cache runs out of storage space

    Explanation: A key collision occurs when unique requests share a cache key, resulting in data overwriting or confusion. Storage limits and TTL problems are unrelated to key collisions. Encryption of data does not cause collisions.

12. Binary vs String Keys

    Why might string-based cache keys be preferred over binary-based cache keys for readability?

    1. Binary keys prevent users from connecting to the cache
    2. String keys slow down every cache operation
    3. String keys are easier for developers to read and debug
    4. Binary keys are universally more efficient

    Explanation: String keys offer better readability, which helps developers understand and troubleshoot cached entries during maintenance. Binary keys are sometimes more space-efficient but not always superior. Slowing cache or preventing connectivity are unrelated to key format.

13. Cache Eviction Policy

    Which is a common policy used to determine which items to remove from a full cache?

    1. Least Recently Used (LRU)
    2. Random Termination Last (RTL)
    3. Most Keyed First (MKF)
    4. First-In-Fixed-Out (FIFO)

    Explanation: LRU removes items that haven't been accessed for the longest time, helping to keep frequently used data available. The other terms are made-up distractors; while FIFO (First-In-First-Out) is a real policy, the option presented is incorrect. MKF and RTL are not real or standard cache eviction policies.

14. Reducing Server Load

    How does effective caching reduce server load in a client-server scenario?

    1. By requiring more memory on the client device
    2. By forcing all clients to refresh data simultaneously
    3. By providing responses directly from the cache, limiting repeated server processing
    4. By disabling data storage entirely

    Explanation: When caching is effective, requests are served from stored data, decreasing the need for the server to process redundant operations. Simultaneous refreshes would actually burden the system, while requiring client memory or disabling storage is not the main purpose of caching.

15. Setting a Cache Key Example

    Given a user profile page for user123, which is a suitable cache key?

    1. cache:page
    2. user:all
    3. passkey:123
    4. user_profile:user123

    Explanation: The key 'user_profile:user123' uniquely identifies the cached data for a specific user profile page. The options 'cache:page' and 'user:all' are too generic and could cause data overlap, while 'passkey:123' is misleading as it does not reference a profile or cache specifically.

16. Benefits of High Cache Hit Rate

    What is a primary benefit of achieving a high cache hit rate in any caching system?

    1. More frequent data corruption
    2. Increased storage costs
    3. Lower network availability
    4. Faster data retrieval for users

    Explanation: A high cache hit rate means more requests are satisfied directly from the cache, significantly speeding up access times. It is not associated with higher costs, network problems, or a greater risk of data corruption, which are incorrect distractors.