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

Test your understanding of basic caching concepts, including Time-to-Live (TTL), cache keys, client-server roles, and typical scenarios. This quiz helps reinforce essential caching terminologies and their correct usage for beginners and professionals in computing.

1. Understanding Cache Basics

   What is the main purpose of a cache in a client-server system?

   1. To permanently delete outdated data from storage
   2. To encrypt all client-server communications automatically
   3. To replace the need for any persistent storage
   4. To temporarily store frequently accessed data for faster retrieval

   Explanation: The main purpose of caching is to temporarily keep frequently accessed data closer to the user or application for quicker access. Unlike permanent storage, a cache is not meant to hold data forever. Encryption is a separate concern and not a direct function of caching. Caching also doesn't eliminate the need for persistent storage, as cached data may expire or be lost.

2. Defining TTL

   What does TTL in caching stand for and what does it control?

   1. Transfer Token Link; it controls cache security
   2. Time To Live; it controls how long data stays in the cache before expiration
   3. Total Transmit Logic; it measures cache access speed
   4. Temporary Table Limit; it restricts the cache size

   Explanation: TTL stands for Time To Live and sets how long a piece of data remains in the cache before being considered expired and removed. The other options refer to unrelated terms or incorrect interpretations of TTL. TTL does not measure speed, does not define cache size directly, and does not handle security tokens.

3. Role of Cache Keys

   In a caching system, what is the primary role of a cache key?

   1. To uniquely identify and retrieve a specific cached item
   2. To store all possible cache values in a single entry
   3. To set network speed for cache retrieval
   4. To encrypt stored data in the cache

   Explanation: A cache key uniquely identifies each cached item so it can be efficiently retrieved. Cache keys do not directly encrypt data or control network speed. A single cache entry does not store all values; each value should have its own specific key.

4. Cache Expiry Example

   If a cached value has a TTL of 60 seconds and was stored at 12:00:00, when will it expire?

   1. At 12:01:00
   2. At 12:01:30
   3. At 12:00:05
   4. At 12:00:30

   Explanation: A TTL of 60 seconds means the data expires exactly one minute after being stored, so at 12:01:00. The other times are either too early or too late and do not match the defined TTL period. TTL is calculated from the moment of storage, not afterward.

5. Cache Miss Scenario

   What happens when a requested item is not found in the cache?

   1. The cache erases all its stored items
   2. The data is automatically created and saved for future use
   3. It is called a cache miss, and the data is fetched from the main source
   4. It is called a cache hit, and the item is returned immediately

   Explanation: When data requested isn't present in the cache, it's called a cache miss, and the system must fetch the data from the original or primary source. A cache hit is the opposite, where the item is found. The cache doesn't erase everything on a miss, and while data may be saved after fetching, it's not done automatically without explicit caching logic.

6. Updating Cached Data

   Which method is commonly used to keep cached data up-to-date with the main source?

   1. Storing data with an infinite TTL
   2. Removing cache keys after each access
   3. Setting an appropriate TTL so data expires and is refreshed
   4. Ignoring cache misses entirely

   Explanation: An appropriate TTL ensures that outdated data is expired and new data is fetched, keeping the cache in sync with the primary source. Storing data indefinitely can lead to stale information. Ignoring misses would defeat the purpose of having a cache, and removing keys after each access would reduce cache effectiveness.

7. Cache Consistency

   Why is it important to choose meaningful and consistent cache keys for storing data?

   1. So the correct data can always be retrieved and overwritten as needed
   2. To increase the physical storage of the cache
   3. To randomly change the TTL of cached items
   4. To make the cache invisible to clients

   Explanation: Meaningful and consistent cache keys make it easier to retrieve and update the right cache entries. Increasing storage or randomly changing TTL is unrelated, and consistent keys do not control client visibility directly.

8. Client-Side Caching

   Which of the following best describes client-side caching in web applications?

   1. Only volatile data is cached on the server
   2. The server never provides any data to the client
   3. Clients encrypt the server’s entire data storage
   4. The client stores copies of data locally to avoid repeated requests for the same resource

   Explanation: Client-side caching allows a client device or browser to keep local copies of resources, reducing network usage and response time. Servers still provide data initially. Server-side volatility and encryption are not directly related to client-side caching.

9. Cache Invalidation Concept

   What does the term 'cache invalidation' refer to?

   1. Encrypting all cached data
   2. Increasing the cache size indefinitely
   3. Duplicating entries for safety
   4. Removing or updating outdated or incorrect entries from the cache

   Explanation: Cache invalidation means clearing out or refreshing data that is no longer accurate. It does not refer to expanding cache storage, duplicating entries, or encryption. Invalidation is about ensuring you don’t serve stale or wrong information.

10. Cache Key Uniqueness

    Why must cache keys be unique for each distinct cached item?

    1. To increase miss rates intentionally
    2. To prevent different items from overwriting each other's data
    3. To minimize TTL values
    4. To allow duplicate retrievals regardless of content

    Explanation: Unique keys ensure each cached piece of data is stored separately, avoiding accidental overwriting. Allowing duplicates would create confusion, and neither TTL values nor increased miss rates are directly influenced by cache key uniqueness.

11. Read and Write Operations

    In a cache system, what is meant by the term 'write-through'?

    1. When data is written only to the cache but not to the main source
    2. When cache content is rewritten every millisecond
    3. When the cache is bypassed for all write operations
    4. When data is written to both the cache and the main data source at the same time

    Explanation: Write-through means all changes go to both cache and the main source, ensuring consistency. Only writing to the cache risks data loss. Frequent rewriting and bypassing the cache do not define the write-through strategy.

12. Common Cache Replacement Policy

    What is a commonly used strategy to decide which cache items to remove when the cache is full?

    1. First Written First Erased (FWFE)
    2. Highest Transmission Link (HTL)
    3. Largest Token Lead (LTL)
    4. Least Recently Used (LRU)

    Explanation: Least Recently Used (LRU) removes the item that has not been accessed for the longest period. The other options are not standard cache eviction strategies, and some are made-up terms.

13. Advantages of Caching

    Which benefit does caching provide in client-server communications?

    1. It increases the frequency of network failures
    2. It reduces response time and server workload
    3. It makes all data transfers fully reliable
    4. It guarantees all data is always up-to-date

    Explanation: Caching speeds up responses and can reduce the work required from the server by serving frequently requested content. It does not increase failures, guarantee perfect data freshness, or make all transfers error-free.

14. Hot and Cold Data

    In caching terminology, what does 'hot data' refer to?

    1. Data that is frequently accessed and likely present in the cache
    2. Data that never changes after being cached
    3. Data that is encrypted before caching
    4. Data stored offsite in a cold storage facility

    Explanation: Hot data is accessed often and usually kept available in the cache for better performance. Encryption status, unchanging data, or offsite storage are unrelated to the 'hot' data concept in caching.

15. Cache Layer Placement

    Where can caching typically be implemented in a client-server architecture?

    1. Solely in the main database
    2. Exclusively within hardware components
    3. On the client, server, or any intermediary layer
    4. Only on the client device

    Explanation: Caching can be placed at many points, including clients, servers, or intermediate proxies, depending on system needs. Limiting cache to just the client, hardware, or database would miss important caching strategies.

16. Cache Hit Rate

    What does a 'cache hit rate' measure in caching systems?

    1. The time to encrypt cached items
    2. The proportion of requests served directly from the cache
    3. The speed at which the server writes to disk
    4. The average size of the cache in bytes

    Explanation: Cache hit rate is the ratio showing how many requests are fulfilled from cached data compared to total requests. It doesn’t indicate cache size, server write speed, or encryption time; those are separate metrics or concerns.