The DBM class provides a wrapper to a Unix-style dbm or Database Manager library.
Dbm databases do not have tables or columns; they are simple key-value data stores, like a Ruby Hash except not resident in RAM. Keys and values must be strings.
The exact library used depends on how Ruby was compiled. It could be any of the following:
The original ndbm library is released in 4.3BSD. It is based on dbm library in Unix Version 7 but has different API to support multiple databases in a process.
Berkeley DB versions 1 thru 6, also known as BDB and Sleepycat DB, now owned by Oracle Corporation.
Berkeley DB 1.x, still found in 4.4BSD derivatives (FreeBSD, OpenBSD, etc).
- gdbm, the GNU implementation of dbm.
- qdbm, another open source reimplementation of dbm.
All of these dbm implementations have their own Ruby interfaces available, which provide richer (but varying) APIs.
Ruby extension for GNU dbm (gdbm) – a simple database engine for storing key-value pairs on disk.
SDBM provides a simple file-based key-value store, which can only store String keys and values.
Note that Ruby comes with the source code for SDBM, while the DBM and GDBM standard libraries rely on external libraries and headers.