Caching System Debugging Quiz Quiz

1. Cache Invalidation Bug

   A caching system stores API responses with a TTL of 60 seconds, but frequently returns stale data; what is the most likely cause?

   1. A. The cache eviction policy is Least Recently Used (LRU).
   2. B. The system clock is incorrectly synchronized leading to inaccuracies with the TTL.
   3. C. The cache size is too small.
   4. D. The API endpoint is returning HTTP 304 Not Modified responses.
   5. E. There is a typo in the TTL configuration set to 60 minutes instead of 60 seconds.

2. Race Condition in Cache Update

   Multiple threads simultaneously attempt to update the same cache entry when it expires, leading to wasted API calls; what is the best solution?

   1. A. Increase the TTL of the cache entries.
   2. B. Implement a write-through caching strategy.
   3. C. Use a distributed lock or compare-and-swap operation to ensure only one thread updates the cache at a time.
   4. D. Disable caching during peak hours.
   5. E. Switch to a larger cache instance with more memory.

3. Cache Key Generation

   A caching system consistently returns the wrong data for different API requests; what debugging step is most important to check?

   1. A. The number of active cache entries.
   2. B. The cache eviction policy implementation.
   3. C. The logic for generating cache keys to ensure they are unique for different API requests.
   4. D. The network bandwidth between the application and the cache.
   5. E. The garbage collection settings in the JVM.

4. Cache Poisoning Vulnerability

   An attacker manages to inject malicious data into the cache, which is then served to legitimate users; what kind of vulnerability is this called?

   1. A. Cache overflow.
   2. B. Cache poisoning.
   3. C. Cache stampede.
   4. D. Cache invalidation.
   5. E. Cache fragmentation.

5. Cache Size Optimization

   A caching system frequently evicts data, even though the total memory usage is low; what could be the problem?

   1. A. The cache eviction policy is Least Frequently Used (LFU).
   2. B. The maximum number of entries allowed in the cache is too low.
   3. C. The TTL of cache entries is set too high.
   4. D. The cache is configured to use disk-based storage instead of memory.
   5. E. The application is experiencing high CPU utilization.

6. Serialization Issue

   When retrieving objects from the cache, the application encounters deserialization errors; what is the most probable cause?

   1. A. The objects are too large to fit in the cache.
   2. B. The class definition has changed since the object was stored in the cache.
   3. C. The cache is using a different character encoding than the application.
   4. D. The cache server is running out of disk space.
   5. E. The firewall is blocking access to the cache server.

7. Cache Stampede Mitigation

   After an API outage, the caching system is overwhelmed by simultaneous requests, causing a 'cache stampede'; what is one effective mitigation strategy?

   1. A. Increase the size of the cache significantly.
   2. B. Use a 'probabilistic early expiration' or 'cache lock' mechanism to prevent simultaneous recomputation of the same value.
   3. C. Disable caching temporarily during outages.
   4. D. Implement a stricter rate limit on API requests.
   5. E. Migrate the cache to a different region.

8. Incorrect TTL Configuration

   The caching system seems to be working, but the API is being called far more often than expected, despite the cache being populated; what configuration item needs verification?

   1. A. The maximum cache size.
   2. B. The eviction policy.
   3. C. The API endpoint's response headers.
   4. D. The time-to-live (TTL) value for cached entries.
   5. E. The network latency between the application and the API.

9. Cache Miss Analysis

   Even with a high hit rate, the application's performance doesn't improve significantly; what is an essential debugging step?

   1. A. Monitor the cache server's CPU usage.
   2. B. Analyze the cache miss patterns to identify what data is not being cached effectively.
   3. C. Optimize the serialization/deserialization process.
   4. D. Reduce the size of cached objects.
   5. E. Upgrade the network card on the cache server.

10. Debugging Concurrent Access

    In a multi-threaded application, retrieving data from the cache intermittently returns null or corrupted data; what is the likely root cause?

    1. A. Insufficient memory allocated to the cache.
    2. B. Lack of proper synchronization mechanisms when accessing the cache from multiple threads.
    3. C. Frequent cache evictions due to low TTL values.
    4. D. Network connectivity issues between the application and the cache.
    5. E. The cache server is using a deprecated version of the operating system.