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Berkeley DB is an embedded database system that supports keyed access to data.
Developers may choose to store data in any of several different storage structures to satisfy the requirements of a particular application. In database terminology, these storage structures and the code that operates on them are called access methods.
The library includes support for the following access methods:
Berkeley DB environment is an encapsulation of one or more databases, log files and shared information about the database environment such as shared memory buffer cache pages.
The transaction subsystem makes operations atomic, consistent, isolated, and durable in the face of system and application failures. The subsystem requires that the data be properly logged and locked in order to attain these properties. Berkeley DB contains all the components necessary to transaction-protect the Berkeley DB access methods and other forms of data may be protected if they are logged and locked appropriately.
A database cursor is a sequential pointer to the database entries. It allows traversal of the database and access to duplicate keyed entries. Cursors are used for operating on collections of records, for iterating over a database, and for saving handles to individual records, so that they can be modified after they have been read.
See also iterators in Acces Methods
The lock subsystem provides interprocess and intraprocess concurrency control mechanisms. While the locking system is used extensively by the Berkeley DB access methods and transaction system, it may also be used as a stand-alone subsystem to provide concurrency control to any set of designated resources.
The logging subsystem is the logging facility used by Berkeley DB. It is largely Berkeley DB specific, although it is potentially useful outside of the Berkeley DB package for applications wanting write-ahead logging support. Applications wanting to use the log for purposes other than logging file modifications based on a set of open file descriptors will almost certainly need to make source code modifications to the Berkeley DB code base.