RocksDB vs Symas LMDB: What are the differences?

Introduction

RocksDB and Symas LMDB are two popular database systems used for different purposes. While RocksDB is an embedded database for storing key-value data, Symas LMDB is a high-performance, memory-mapped key-value store. Despite their similarities as key-value databases, there are several key differences between the two. This article will outline and explain the six main differences between RocksDB and Symas LMDB.

1. Storage Type: RocksDB stores data on disk, making it suitable for applications with large data sets that cannot fit entirely in memory. In contrast, Symas LMDB stores data in memory-mapped files, providing fast and efficient access to data that fits into the available memory.

2. Write Amplification: RocksDB implements a log-structured merge-tree (LSM) data structure, which can cause write amplification. This means that writes can result in multiple disk operations, leading to increased disk activity and slower performance. On the other hand, Symas LMDB uses a B+ tree-like structure, which avoids write amplification, resulting in faster write performance.

3. Durability: RocksDB provides durability by writing data to disk at the cost of slower write performance. In contrast, Symas LMDB provides durability by syncing data to disk asynchronously, allowing for faster writes.

4. Concurrency Control: RocksDB uses a locking mechanism for concurrency control, which can lead to contention and decrease performance in highly concurrent workloads. On the other hand, Symas LMDB uses multi-version concurrency control (MVCC), which allows for better scalability and performance in concurrent environments.

5. Memory Usage: RocksDB utilizes more memory for its internal structures, such as memtable and block cache, leading to higher memory consumption. In contrast, Symas LMDB is designed to be memory-efficient and can operate with smaller memory footprints.

6. Development Language: RocksDB is primarily written in C++ and provides language bindings for various programming languages. Symas LMDB is written in C and provides language bindings for several programming languages, making it accessible to a wider range of developers.

In summary, RocksDB is a disk-based key-value store suitable for large data sets that cannot fit entirely in memory, while Symas LMDB is a memory-mapped key-value store with high-performance characteristics. RocksDB has write amplification, slower writes, and uses more memory, while Symas LMDB provides faster writes, lower memory usage, and utilizes a MVCC concurrency control mechanism.