Redis Interview Questions and Answers for 10 years experience

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100 Redis Interview Questions and Answers (10+ years experience)

  1. What are the different Redis data structures and when would you use each?

    • Answer: Redis offers various data structures: Strings (simple key-value pairs, ideal for caching), Lists (ordered collections, good for queues and stacks), Sets (unordered collections of unique elements, useful for membership testing), Sorted Sets (sets with scores, perfect for leaderboards and range queries), Hashes (key-value pairs within a key, representing objects), Bitmaps (efficient for storing boolean data), HyperLogLogs (approximate cardinality estimation), Geospatial indices (for location-based queries), Streams (append-only logs for event processing). The choice depends on the specific application needs. For instance, caching uses strings, message queues use lists, and leaderboards use sorted sets.

  2. Explain the concept of Redis persistence. Discuss AOF and RDB.

    • Answer: Redis persistence ensures data durability. RDB (Redis Database) creates point-in-time snapshots. It's fast but can lead to data loss if a crash occurs between snapshots. AOF (Append Only File) logs every write operation. It's slower but provides better data safety. Choosing between them depends on the acceptable trade-off between speed and data safety. Hybrid approaches (using both) are also common.

  3. How does Redis handle memory management?

    • Answer: Redis uses an in-memory data store. It employs efficient memory allocation strategies to minimize fragmentation and optimize performance. Memory usage is directly related to the dataset size. Redis also offers eviction policies (like LRU, LFU) to manage memory when it's full, evicting less frequently used data.

  4. Describe Redis clustering and its advantages.

    • Answer: Redis Cluster allows scaling Redis beyond the capacity of a single instance by distributing data across multiple nodes. Advantages include high availability, scalability, and fault tolerance. Data is partitioned across slots, ensuring data distribution and redundancy. It handles node failures gracefully by automatically redistributing data.

  5. Explain Redis transactions.

    • Answer: Redis transactions provide atomicity for a series of commands. They ensure that either all commands within a transaction are executed, or none are. `MULTI`, `EXEC`, `DISCARD`, and `WATCH` are key commands. `WATCH` enables optimistic locking, preventing conflicts if data changes during the transaction.

  6. What are Redis Pub/Sub and its applications?

    • Answer: Redis Pub/Sub (Publish/Subscribe) is a messaging system where publishers send messages to channels, and subscribers listen to those channels. Applications include real-time dashboards, chat applications, and distributed systems communication. It's lightweight and efficient for asynchronous communication.

  7. How do you optimize Redis performance?

    • Answer: Optimization involves various strategies: choosing appropriate data structures, using efficient commands, optimizing client-side code, configuring proper persistence options, using connection pooling, employing clustering for scalability, and monitoring performance metrics (CPU, memory, network).

  8. Explain Redis Sentinel.

    • Answer: Redis Sentinel provides high availability for Redis instances. It monitors the health of master nodes and automatically performs failover to a slave node if the master fails. It also manages configuration and provides a single point of access for clients.

  9. Discuss different Redis eviction policies.

    • Answer: When memory is full, Redis uses eviction policies to remove data. Common policies include: Noeviction (reject writes), Allkeys-LRU (least recently used), Allkeys-LFU (least frequently used), Volatile-LRU (LRU for volatile keys), Volatile-LFU (LFU for volatile keys), Volatile-TTL (remove expiring keys first), Random (random key eviction). The choice depends on application requirements.

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