YoctoDB is an embedded database engine with the following major features:

• Java 8
• Depends on Guava only
• Immutable after construction
• Optionally partitioned
• Space-efficient
• Flat document-oriented
• Indexed fields for filtering/sorting
• Embedded
• mmap'ed (ByteBuffer'ed)

See Project Wiki:

• Getting Started Guide
• Motivation
• Design
• Internal Benchmarks

Contact us through YoctoDB User Group.