Redis Interview Questions
- What is Redis and what are its use cases?
Answer: Redis is an open-source, in-memory data structure store that can be used as a database, cache, and message broker. Its use cases include caching, real-time analytics, leaderboards, and task queues.
- What is the difference between Redis and other databases?
Answer: Redis is an in-memory database, which means that data is stored in memory rather than on disk. This makes Redis much faster than traditional disk-based databases, but also means that it has limited capacity.
- How is Redis different from Memcached?
Answer: Both Redis and Memcached are in-memory data stores, but Redis is more feature-rich and can be used as a database, cache, and message broker. Memcached is more focused on caching.
- What is the difference between SET and GET in Redis?
Answer: The SET command is used to set a value in Redis, while the GET command is used to retrieve a value from Redis.
- What is a Redis key?
Answer: A Redis key is a string that is used to identify a value in Redis.
- What is Redis persistence?
Answer: Redis persistence refers to the ability of Redis to store data to disk, either by regularly saving snapshots of the data or by appending each command to a log.
- What is a Redis cluster?
Answer: A Redis cluster is a group of Redis instances that work together to provide high availability and scalability.
- How can you improve Redis performance?
Answer: Redis performance can be improved by using pipelining, reducing the number of round trips to Redis, and using Redis in cluster mode.
- What is the role of Redis pub/sub?
Answer: Redis pub/sub is a messaging system that allows publishers to send messages to multiple subscribers.
- What is a Lua script in Redis?
Answer: A Lua script in Redis is a script that can be executed on the Redis server. Lua scripts can be used to perform complex operations on data in Redis.
- What is a Redis transaction?
Answer: A Redis transaction is a group of commands that are executed as a single atomic operation.
- What is the difference between Redis LIST and SET?
Answer: Redis LIST is an ordered collection of strings, while SET is an unordered collection of strings.
- What is the TTL in Redis?
Answer: The TTL (time to live) in Redis is the amount of time that a key/value pair will remain in the Redis cache before it is automatically deleted.
- What is a Redis pipeline?
Answer: A Redis pipeline is a mechanism that allows multiple commands to be sent to Redis at once, reducing the number of round trips and improving performance.
- What is Redis Sentinel?
Answer: Redis Sentinel is a high-availability solution for Redis that monitors Redis instances and automatically promotes a new master if the current master fails.
- What is the difference between Redis hash and Redis string?
Answer: Redis hash is a key/value store, while Redis string is a simple key/value store that can only store string values.
- What is the Redis RDB file format?
Answer: The Redis RDB file format is a binary file format used to persist Redis data to disk.
- What is the Redis AOF file format?
Answer: The Redis AOF (append-only file) file format is a log-based file format used to persist Redis data to disk.
- What is the ZSET in Redis?
Answer: ZSET (sorted set) is a Redis data type that stores a collection of unique elements with scores, which can be sorted by the score.
- What is Redis Bloom filter?
Answer: Redis Bloom filter is a probabilistic data structure that is used to test whether an element is a member of a set or not.
- What is the difference between Redis and MongoDB?
Answer: Redis is an in-memory data structure store, while MongoDB is a document-oriented database. Redis is more suited for caching and real-time analytics, while MongoDB is better for storing structured data.
- What is Redis cache?
Answer: Redis cache is a caching mechanism that uses Redis as a cache store to improve the performance of an application.
- How can you ensure data consistency in a Redis cluster?
Answer: Data consistency in a Redis cluster can be ensured by using Redis transactions, enabling Redis Sentinel, and using Redis cluster mode.
- What is the Redis GEO command?
Answer: The Redis GEO command is used to store and query geographical data in Redis.
- What is the Redis LRU policy?
Answer: The Redis LRU (least recently used) policy is used to evict data from the Redis cache based on the last time it was accessed.
- What is the Redis EXPIRE command?
Answer: The Redis EXPIRE command is used to set a TTL (time to live) on a key in Redis, after which it will be automatically deleted.
- What is the Redis SCAN command?
Answer: The Redis SCAN command is used to iterate over keys in Redis without blocking the server.
- What is Redis Lua scripting?
Answer: Redis Lua scripting allows users to write custom scripts in Lua that can be executed in Redis.
- What is Redis Sentinel?
Answer: Redis Sentinel is a built-in high-availability solution for Redis that monitors Redis instances and promotes a new master if the current master fails.
- What is the Redis ZRANGE command?
Answer: The Redis ZRANGE command is used to retrieve a range of elements from a sorted set in Redis.
- What is the Redis EVAL command?
Answer: The Redis EVAL command is used to execute a Lua script on the Redis server.
- What is the Redis SADD command?
Answer: The Redis SADD command is used to add one or more members to a set in Redis.
- What is Redis partitioning?
Answer: Redis partitioning is the process of splitting data across multiple Redis instances to improve performance and scalability.
- What is the Redis PUBLISH command?
Answer: The Redis PUBLISH command is used to publish a message to all subscribers of a channel in Redis pub/sub.
- What is the Redis INFO command?
Answer: The Redis INFO command is used to retrieve information about the Redis instance, such as memory usage and server statistics.
- What is the Redis RENAME command?
Answer: The Redis RENAME command is used to rename a key in Redis.
- What is the Redis BITCOUNT command?
Answer: The Redis BITCOUNT command is used to count the number of set bits in a string in Redis.
- What is Redis pipelining?
Answer: Redis pipelining is a mechanism that allows multiple commands to be sent to Redis in a single network request, improving performance.
- What is the Redis KEYS command?
Answer: The Redis KEYS command is used to retrieve a list of all keys in Redis that match a specified pattern. However, it should be used with caution as it can impact the performance of Redis.
- What is Redis cluster?
Answer: Redis cluster is a distributed implementation of Redis that allows data to be partitioned across multiple nodes for improved performance and scalability.
- What is Redis RDB?
Answer: Redis RDB (Redis DataBase) is a persistence mechanism that allows Redis to save its data to disk.
- What is Redis AOF?
Answer: Redis AOF (Append-Only File) is a persistence mechanism that logs every write operation to a file, allowing Redis to recover from a crash or restart.
- What is Redis mass insertion?
Answer: Redis mass insertion is a technique used to load large amounts of data into Redis quickly.
- What is the Redis ZRANGEBYLEX command?
Answer: The Redis ZRANGEBYLEX command is used to retrieve a range of elements from a sorted set in Redis using lexicographic ordering.
- What is Redis SCANCOUNT?
Answer: Redis SCANCOUNT is a parameter that can be used with the Redis SCAN command to control the number of keys returned per iteration.
- What is Redis pipeline?
Answer: Redis pipeline is a mechanism that allows multiple commands to be queued up and sent to Redis in a single operation, improving performance.
- What is Redis Pub/Sub?
Answer: Redis Pub/Sub is a messaging system in Redis that allows subscribers to receive messages published to a channel by a publisher.
- What is Redis blocking?
Answer: Redis blocking is a feature that allows Redis clients to wait for new messages or data to arrive without polling the server continuously.
- What is Redis multi?
Answer: Redis multi is a command that allows multiple Redis commands to be executed as a single transaction, ensuring that either all of the commands are executed or none of them.
- What is Redis hyperloglog?
Answer: Redis hyperloglog is a probabilistic data structure that is used to estimate the cardinality of a set, even when it is too large to be stored in memory.
- What is Redis SCAN MATCH?
Answer: Redis SCAN MATCH is a parameter that can be used with the Redis SCAN command to match keys that contain a specified pattern.
- What is Redis FLUSHDB?
Answer: The Redis FLUSHDB command is used to delete all keys in the current Redis database.
- What is Redis PEXPIRE?
Answer: The Redis PEXPIRE command is used to set a TTL (time to live) on a key in Redis, after which it will be automatically deleted, using a timestamp in milliseconds.
- What is Redis SORT?
Answer: The Redis SORT command is used to sort the elements of a list, set, or sorted set in Redis.
- What is Redis SMEMBERS?
Answer: The Redis SMEMBERS command is used to retrieve all members of a set in Redis.
- What is Redis BITOP?
Answer: The Redis BITOP command is used to perform bitwise operations on strings in Redis.
- What is Redis EVALSHA?
Answer: The Redis EVALSHA command is used to execute a precompiled Lua script in Redis.
- What is Redis LUA?
Answer: Redis LUA is a built-in Lua interpreter in Redis that allows users to execute custom scripts in Redis.
- What is Redis SCAN TYPE?
Answer: Redis SCAN TYPE is a parameter that can be used with the Redis SCAN command to match keys of a specific type, such as string, hash, list, set, or sorted set.
- What is Redis Lua scripting?
Answer: Redis Lua scripting is a feature that allows users to run custom scripts in Redis using the Lua programming language.
- What is Redis Lua REPL?
Answer: Redis Lua REPL (Read-Eval-Print Loop) is a command-line interface that allows users to interactively test and debug Lua scripts in Redis.
- What is Redis Sentinel?
Answer: Redis Sentinel is a high-availability feature in Redis that allows automatic failover and monitoring of Redis instances in a cluster.
- What is Redis client-side caching?
Answer: Redis client-side caching is a technique that allows clients to cache Redis data locally to improve performance and reduce network traffic.
- What is Redis cache eviction policy?
Answer: Redis cache eviction policy is a mechanism that determines which keys to delete when Redis runs out of memory.
- What is Redis slow log?
Answer: Redis slow log is a feature that records Redis commands that take longer than a specified threshold to execute, helping developers identify and optimize slow commands.
- What is Redis cluster mode?
Answer: Redis cluster mode is a feature that allows Redis to be deployed in a distributed environment, with data partitioned across multiple nodes.
- What is Redis replication?
Answer: Redis replication is a feature that allows Redis to create one or more copies of a database for high availability and data durability.
- What is Redis pipelining?
Answer: Redis pipelining is a technique that allows clients to send multiple Redis commands to the server in a single network packet, improving performance.
- What is Redis Lua script caching?
Answer: Redis Lua script caching is a feature that allows Redis to cache precompiled Lua scripts to improve performance.
- What is Redis memory optimization?
Answer: Redis memory optimization is a process of reducing the memory footprint of Redis, improving performance and scalability.
- What is Redis memory fragmentation?
Answer: Redis memory fragmentation is a problem that occurs when Redis allocates and deallocates memory frequently, leading to unused memory that cannot be reclaimed by the operating system.
- What is Redis replication lag?
Answer: Redis replication lag is a delay that occurs when a replica server is behind the primary server in terms of data updates.
- What is Redis load balancing?
Answer: Redis load balancing is a technique that distributes Redis client requests across multiple Redis instances to improve performance and availability.
- What is Redis virtual memory?
Answer: Redis virtual memory is a feature that allows Redis to store data on disk when the available memory is not sufficient, without affecting the performance of Redis.
- What is Redis data sharding?
Answer: Redis data sharding is a technique that partitions large data sets across multiple Redis instances to improve performance and scalability.
- What is Redis blocking pop operation?
Answer: Redis blocking pop operation is a feature that allows Redis clients to block until an item is available in a queue or list.
- What is Redis eviction policy?
Answer: Redis eviction policy is a mechanism that determines which keys to delete when Redis runs out of memory.
- What is Redis pipelining and how does it work?
Answer: Redis pipelining is a technique that allows multiple Redis commands to be sent to the server in a single network packet, reducing network overhead and improving performance. Clients can send multiple commands to the server and then wait for the results to be returned in a single response.
- What is Redis data persistence and how does it work?
Answer: Redis data persistence is a feature that allows Redis to save its data to disk or another storage device, ensuring that data is not lost in the event of a crash or power failure. Redis supports two persistence mechanisms: RDB and AOF. RDB saves a snapshot of the data
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