AcornDB
AcornDB is a high performance, small footprint, transactional object oriented database written entirely in Java. It stores data in the application's native format, so no runtime data translation is required. AcornDB supports full ACID transactions and recovery. It provides an easy-to-use interface like query-by-example, object query API, automatic class schema recognition allowing programmers to store and retrieve information quickly, simply and reliably. AcornDB enabling high concurrency and speed while providing ACID transactions. AcornDB efficiently caches the data in memory, without exceeding application-specified limits. In this way works with an application to use available JVM resources while providing access to very large data sets.
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License
GNU General Public License (GPL)