Prevayler

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Prevayler is an open-source, BSD-licensed layer for Java that makes in-memory data durable. It keeps your Java objects in RAM and saves the system state by taking snapshots through object serialization. If the system crashes, Prevayler loads the last snapshot to restore state. Data changes happen as transactions on serializable Java objects. Because everything runs in memory and in-process, read operations are typically three to four orders of magnitude faster than traditional databases. Prevayler requires enough RAM to hold the entire system state. It was started by Klaus Wuestefeld.