Redis vs VoltDB: What are the differences?

Introduction

Redis and VoltDB are both popular in-memory databases used for different purposes. While Redis is a key-value store primarily used for caching and persistent storage, VoltDB is an in-memory relational database that focuses on high-speed transaction processing. Let's explore the key differences between Redis and VoltDB.

1. Data Model: Redis stores data as key-value pairs, allowing various data types such as strings, lists, sets, hashes, and sorted sets. On the other hand, VoltDB supports a relational data model with tables, rows, and columns, enabling more complex data structures and relationships.

2. ACID Compliance: Redis is not strictly ACID compliant as it sacrifices durability for performance, making it suitable for scenarios where data loss can be tolerated. In contrast, VoltDB fully adheres to the ACID (Atomicity, Consistency, Isolation, Durability) principles, ensuring data integrity at all times.

3. Scaling Strategy: Redis can be scaled horizontally using clustering techniques, allowing data to be distributed across multiple nodes. In VoltDB, scaling is achieved through shared-nothing partitioning, where data is partitioned across different servers to ensure high availability and performance.

4. Concurrency Control: Redis provides simple concurrency control mechanisms such as optimistic locking and transactions. VoltDB, on the other hand, employs a distributed concurrency control mechanism called serializable snapshot isolation (SSI), ensuring consistent and serializable execution of transactions.

5. Use Cases: Redis is often used for caching, session management, real-time analytics, and pub/sub messaging due to its fast read and write performance. VoltDB, with its strong ACID compliance and high-speed transaction processing capabilities, is well-suited for applications that require high-volume data ingestion, real-time decision-making, and fraud detection.

6. Durability and Persistence: Redis supports different levels of persistence, including snapshots and append-only logs. However, it primarily relies on an in-memory storage approach, which means that data can be lost in the event of a system crash. In contrast, VoltDB provides durable storage by replicating data across multiple servers, ensuring no data loss even in failure scenarios.

In summary, Redis and VoltDB differ in their data models, ACID compliance, scaling strategies, concurrency control mechanisms, use cases, and durability approaches. Redis offers a flexible key-value store for caching and persistent storage, while VoltDB focuses on high-speed transaction processing with a relational data model.