Berkeley DB

Berkeley DB (BDB) is a software library intended to provide a high-performance embedded database for key/value data. Berkeley DB is written in C with API bindings for C++, C#, Java, Perl, PHP, Python, Ruby, Smalltalk, Tcl, and many other programming languages. BDB stores arbitrary key/data pairs as byte arrays, and supports multiple data items for a single key. Berkeley DB is not a relational database[1] although it has advanced database features including database transactions, multiversion concurrency control and write-ahead logging.

Berkeley DB
Original author(s)Margo Seltzer and Keith Bostic of Sleepycat Software
Developer(s)Sleepycat Software, later Oracle Corporation
Initial release1994 (1994)
Stable release
18.1 (Core) / JE (7.5) / June 14, 2018 (2018-06-14)
Written inC
Operating systemWindows, Unix-like
Size~1244 kB compiled on Windows x86
TypeEmbedded database, NoSQL Database
LicenseDual licensed (GNU Affero General Public License and commercial permissive license) (version 6.x and upwards)
Sleepycat license (versions 2.0-5.x)
4-clause BSD license (versions 1.x) / JE is licensed under Apache License, Version 2.0.
Websitewww.oracle.com/database/berkeley-db/

BDB can support thousands of simultaneous threads of control or concurrent processes manipulating databases as large as 256 terabytes,[2] on a wide variety of operating systems including most Unix-like and Windows systems, and real-time operating systems.

BDB was commercially supported and developed by Sleepycat Software from 1996 to 2006. This company was acquired by Oracle Corporation in February 2006, which continues to develop and sell Berkeley DB products.

Origin

Berkeley DB originated at the University of California, Berkeley as part of BSD, Berkeley's version of the Unix operating system. After 4.3BSD (1986), the BSD developers attempted to remove or replace all code originating in the original AT&T Unix from which BSD was derived. In doing so, they needed to rewrite the Unix database package.[3] Seltzer and Yigit[4] created a new database, unencumbered by any AT&T patents: an on-disk hash table that outperformed the existing dbm libraries. Berkeley DB itself was first released in 1991 and later included with 4.4BSD.[3] In 1996 Netscape requested that the authors of Berkeley DB improve and extend the library, then at version 1.86, to suit Netscape's requirements for an LDAP server[5] and for use in the Netscape browser. That request led to the creation of Sleepycat Software. This company was acquired by Oracle Corporation in February 2006, which continues to develop and sell Berkeley DB.

Since its initial release, Berkeley DB has gone through various versions. Each major release cycle has introduced a single new major feature generally layering on top of the earlier features to add functionality to the product. The 1.x releases focused on managing key/value data storage and are referred to as "Data Store" (DS). The 2.x releases added a locking system enabling concurrent access to data. This is what is known as "Concurrent Data Store" (CDS). The 3.x releases added a logging system for transactions and recovery, called "Transactional Data Store" (TDS). The 4.x releases added the ability to replicate log records and create a distributed highly available single-master multi-replica database. This is called the "High Availability" (HA) feature set. Berkeley DB's evolution has sometimes led to minor API changes or log format changes, but very rarely have database formats changed. Berkeley DB HA supports online upgrades from one version to the next by maintaining the ability to read and apply the prior release's log records.

The FreeBSD and OpenBSD operating systems continue to use Berkeley DB 1.8x for compatibility reasons;[6] Linux-based operating systems commonly include several versions to accommodate for applications still using older interfaces/files.

Starting with the 6.0.21 (Oracle 12c) release, all Berkeley DB products are licensed under the GNU AGPL.[7][8] Berkeley DB JE 7.3.7 is licensed under the Apache License, Version 2.0. Previously, Berkeley DB was redistributed under the 4-clause BSD license (before version 2.0), and the Sleepycat Public License, which is an OSI-approved open-source license as well as an FSF-approved free software license.[9][10] The product ships with complete source code, build script, test suite, and documentation. The code quality and general utility along with the licensing terms have led to its use in a multitude of free and open-source software. Those who do not wish to abide by the terms of the GNU AGPL, or use an older version with the Sleepycat Public License, have the option of purchasing another proprietary license for redistribution from Oracle Corporation. This technique is called dual licensing. Different versions of Berkeley DB (DB, JE, XML) may have different licensing terms.

Berkeley DB includes compatibility interfaces for some historic Unix database libraries: dbm, ndbm and hsearch (a System V and POSIX library for creating in-memory hash tables).[11]

Architecture

Berkeley DB has an architecture notably simpler than that of other database systems like relational database management systems. For example, like SQLite, it is not based on a server/client model, and does not provide support for network access – programs access the database using in-process API calls. Oracle added support for SQL in 11g R2 release based on the popular SQLite API by including a version of SQLite in Berkeley DB (it uses Berkley DB for storage).[12] There is third party support for PL/SQL in Berkeley DB via a commercial product named Metatranz StepSqlite.[13]

A program accessing the database is free to decide how the data is to be stored in a record. Berkeley DB puts no constraints on the record's data. The record and its key can both be up to four gigabytes long.

Despite having a simple architecture, Berkeley DB supports many advanced database features such as ACID transactions, fine-grained locking, hot backups and replication.

Editions

The name "Berkeley DB" is given to three different products:[14]

  1. Berkeley DB – the current version as of June 2018 is 18.1.
  2. Berkeley DB Java Edition – the current version as of November 2017 is 7.5.11
  3. Berkeley DB XML – the current version as of November 2017 is 6.1.4

Each edition has separate database libraries, despite the common branding. The first is the traditional Berkeley DB, written in C. It contains several database implementations, including a B-tree and one built around extensible hashing. It supports multiple language bindings, including C/C++, Java (via JNI), C# .NET, Perl and Python.

Berkeley DB Java Edition (JE) is a pure Java database management library. Its design resembles that of Berkeley DB without replicating it exactly, and has a feature set that includes many of those found in the traditional Berkeley DB and others that are specific to the Java Edition. It has a log structured storage architecture, which gives it different performance and concurrency characteristics. Three APIs are available – a Direct Persistence Layer which is "Plain Old Java Objects" (POJO); one which is based on the Java Collections Framework (an object persistence approach); and one based on the traditional Berkeley DB API. The Berkeley DB Java Edition High Availability option (Replication) is available. Note that traditional Berkeley DB also supports a Java API, but it does so via JNI and thus requires an installed native library.

The Berkeley DB XML database specializes in the storage of XML documents, supporting XQuery via XQilla. It is implemented as an additional layer on top of (a legacy version of) Berkeley DB and the Xerces library. DB XML is written in C++ and supports multiple language bindings, including C++, Java (via JNI), Perl and Python.

Programs that use Berkeley DB

Berkeley DB provides the underlying storage and retrieval system of several LDAP servers, database systems, and many other proprietary and free/open source applications. Notable software that use Berkeley DB for data storage include:

  • Bitcoin Core – The first implementation of the Bitcoin cryptocurrency retains use of 2009 Berkeley DB 4.8 for one feature[15]
  • Bogofilter – A free/open source spam filter that saves its wordlists using Berkeley DB by default[16]
  • Carbonado – An open source relational database access layer that can optionally use Berkeley DB[17]
  • Citadel – A free/open source groupware platform that keeps all of its data stores, including the message base, in Berkeley DB
  • Jabberd2 – An XMPP server
  • KDevelop – An IDE for Unix-like operating systems
  • Oracle NoSQL – A NoSQStill uses Berkeley DB 4.8 from 2009 for the walletL distributed key-value database
  • Oracle Retail Predictive Application Server (RPAS) - A platform used by Oracle Retail to implement solutions for Retail Financial Planning, Merchandise Planning/Ranging, and Supply Chain Planning
  • Sendmail – A popular MTA for Linux/Unix systems
  • Spamassassin – An anti-spam application
  • Sun Grid Engine – A free and open-source distributed resource management system
  • Voldemort – A NoSQL distributed key-value database that can optionally use BDB as a backend store[18][19]

Past users
  • OrangeFS – A parallel file system for HPC clusters in the process of deprecating BDB in favour of LMDB[20]
  • RPM – The RPM Package Manager is deprecating Berkeley DB in favour of SQLite [21]
  • memcacheDB – A persistence-enabled variant of memcached. MemcacheDB has not been maintained since 2009 and has been dropped by major Linux distributions.
  • Evolution – A free/open source mail client; BDB addressbook.db was deprecated in favour of SQLite contacts.db
  • MySQL database system – MySQL included a BDB data storage backend prior to v5.1
  • Exim – An MTA developed at the University of Cambridge for use on Unix systems connected to the internet. Deprecated in favor of LMDB
  • Cyrus IMAP Server – A free/open source IMAP and POP3 server, developed by Carnegie Mellon University. Deprecated in favor of LMDB
  • OpenLDAP – A free/open source implementation of the Lightweight Directory Access Protocol (LDAP). Deprecated in favor of LMDB
  • OrangeFS – An open-source parallel file system, the next generation of Parallel Virtual File System. Deprecated in favor of LMDB
  • Postfix – A fast, secure, easy-to-administer MTA for Linux/Unix systems. Deprecated in favor of LMDB
  • Subversion – A centralized version control system. Deprecated in favor of FSFS
  • GlusterFS – Prior to v3.4, GlusterFS included a BDB storage translator

Licensing

Berkeley DB V2.0 and higher is available under a dual license:

  1. Oracle commercial license with professional support[22]
  2. Open source license

The switch to AGPL has caused major GNU/Linux distributions such as Debian to completely phase out their use of Berkeley DB, with a preference for Lightning Memory-Mapped Database (LMDB). The rationale is that having commercial users use AGPL code would be unacceptable, as they would be forced to provide their source code to users by a simple software upgrade.[24]

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See also

References
  1. Berkeley DB Reference Guide: What is Berkeley DB not?. Doc.gnu-darwin.org (2001-05-31). Retrieved on 2013-09-18.
  2. http://doc.gnu-darwin.org/am_misc/dbsizes.html Berkeley DB Reference Guide: Database limits Retrieved on 2013-09-19
  3. Olson, Michael A.; Bostic, Keith; Seltzer, Margo (1999). "Berkeley DB" (PDF). Proc. FREENIX Track, USENIX Annual Tech. Conf. Retrieved October 20, 2009.
  4. Seltzer, Margo; Yigit, Ozan (1991). "A New Hashing Package for UNIX". Proc. USENIX Winter Tech. Conf. Retrieved October 20, 2009.
  5. Brunelli, Mark (March 28, 2005). "A Berkeley DB primer". Enterprise Linux News. Retrieved December 28, 2008.
  6. "db(3)". Retrieved April 12, 2009.
  7. [Berkeley DB Announce] Major Release: Berkeley DB 12gR1 (12.1.6.0). Retrieved July 5, 2013. (Despite AGPL mentions there, the source archive still declares BSD-4-Clause terms in 6.0.19.)
  8. Snapshot of the 6.0.19 source at the time
  9. "The Sleepycat License". Open Source Initiative. October 31, 2006. Retrieved December 28, 2008.
  10. "Licenses". Free Software Foundation. December 10, 2008. Archived from the original on December 16, 2008. Retrieved December 28, 2008.
  11. "Compatibility with historic UNIX interfaces". docs.oracle.com. Retrieved 2019-11-20.
  12. "Twitter / Gregory Burd: @humanications We didn't r ..."
  13. "Official Berkeley DB FAQ". Oracle Corporation. Retrieved March 30, 2010. Does Berkeley DB support PL/SQL?
  14. Oracle Berkeley DB Downloads: Latest Production Releases
  15. Release Notes for Bitcoin 0.8.0 2013
  16. "bogofilter -- Fast Bayesian Spam Filter / Code (Git) / [93b68e] /bogofilter/README". sourceforge.net. Retrieved 2020-07-17.
  17. Github project Carbonado/Carbonado, Carbonado, 2020-04-04, retrieved 2020-07-17
  18. "Voldemort source code package which includes the BDB integration". GitHub. Retrieved 2017-03-16.
  19. "Design - Voldemort". www.project-voldemort.com. Retrieved 2020-07-17.
  20. "LMDB is a newer and preferred database backend option but is not yet the default."
  21. Change format of the RPM database from Berkeley DB to a new Sqlite format.
  22. "Download, license and sales information". Nov 30, 2017.
  23. "Major Release: Berkeley DB 12gR1 (12.1.6.0)". June 10, 2013. Retrieved July 15, 2013.
  24. Ondřej Surý (June 19, 2014). "New project goal: Get rid of Berkeley DB (post jessie)". debian-devel (Mailing list). Debian.
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