key-value store suggestion

Question

I need a very basic key-value store for java. I started with a HashMap but it seems that HashMap is somewhat space inefficient (I\'m storing ~20 million records, and seems t

Answer 1

Just wanted to reference some more open source options that became available over time since this question was first asked.

Apache 2, BTree, Apache Directory Project JDBM replacement effort:

http://directory.apache.org/mavibot/

MPL2/EPL1, RTree, MVStore, H2 Storage Engine:

http://www.h2database.com/html/mvstore.html

Apache 2, Xodus Environments, JetBrains YouTrack and Hub storage engine:

https://github.com/JetBrains/xodus