NuDB is an append-only, key/value store specifically optimized for random read performance on modern SSDs or equivalent high-IOPS devices.
The most common application for NuDB is content addressable storage where a cryptographic digest of the data is used as the key.
The read performance and memory usage are independent of the size of the database. These are some other features:

Low memory footprint
Database size up to 281TB
All keys are the same size
Append-only, no update or delete
Value sizes from 1 to 2^32 bytes (4GB)
Performance independent of growth
Optimized for concurrent fetch
Key file can be rebuilt if needed
Inserts are atomic and consistent
Data file may be efficiently iterated
Key and data files may be on different devices
Hardened against algorithmic complexity attacks
Header-only, no separate library to build
Requirements:

Boost 1.58 or higher
C++11 or greater
SSD drive, or equivalent device with high IOPS