Redis vs RocksDB: What are the differences?

Redis is an in-memory data structure store known for its speed and versatility, while RocksDB is an embedded key-value store optimized for fast storage on flash devices. Let's explore the key differences between them.

1. Data Storage and Durability: Redis is primarily an in-memory data store, where data is stored in RAM for fast access. It supports optional persistence through snapshots or logs, but the primary focus is on fast in-memory operations. On the other hand, RocksDB is an on-disk data store, where data is stored in persistent storage. It offers durability guarantees by writing data to disk and ensures data integrity even in the face of system failures.

2. Data Access Patterns: Redis is optimized for high-throughput, low-latency operations by keeping the entire working dataset in RAM. It provides a wide range of data structures and supports operations like string manipulation, list manipulation, and pub/sub messaging. RocksDB, on the other hand, is suitable for applications that require large-scale data persistence. It is designed to handle high write throughput and supports random reads and writes efficiently.

3. Scalability: Redis is primarily a single-node database, but it provides replication and clustering mechanisms to achieve high availability and scale. With Redis, you can replicate data across multiple nodes and use Redis Cluster for horizontal scaling. RocksDB, on the other hand, is a library that can be used as part of a distributed database system, such as Apache HBase or Apache Cassandra, to improve their performance and durability.

4. Data Size Limitation: Redis is limited by the amount of RAM available in a single node. If the dataset exceeds the available RAM, it will start swapping to disk, which can significantly impact performance. In contrast, RocksDB does not have a strict limitation on the dataset size since it can store data on disk. However, the performance of random reads and writes may degrade if the dataset size exceeds the available RAM for caching frequently accessed data.

5. Consistency Guarantees: Redis provides eventual consistency, which means that after a write operation, the updates may take some time to propagate to all replicas in a replication setup. RocksDB offers strict consistency guarantees by ensuring that the data written to disk is immediately durable and consistent across all replicas.

In summary, Redis is optimized for fast in-memory operations and real-time data access, while RocksDB is designed for high-throughput data persistence and on-disk storage. Redis is suitable for applications with smaller datasets and low-latency requirements, whereas RocksDB is more suitable for applications that require scalable data storage with durability guarantees.