Cristoph Rupp's hamsterdb is a lightweight, embedded database engine designed for ease of use, high performance, stability, and portability. In the database world, you have typically two extremes. On the high end, you have the full-featured and sometimes unwieldy Relational DBMS with SQL and a daemon/server process (such as Oracle). On the low end, there are b+tree-based systems, which are essentially just a database engine that is linked into the application and usually are without SQL support. As a lightweight database engine, hamsterdb fits into the latter category. It is very fast, but only supports the minimum needed operations. Specifically, it is embeddable, and therefore does not have the external dependencies or installation hassles of an SQL server. It is simply a database engine, but not a database management system (DBMS) and it has no relational functions or other features provided by SQL. For many apps that need to manage a lot of data, but don't need an externally accessible database for report writers or 3rd party tools, hamsterdb may be your "pet" solution.
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