### Berkeley DB Reference Guide: Introduction |

### What other services does Berkeley DB provide?

Berkeley DB also provides core database services to developers. These services include:

Page cache management:
  The page cache provides fast access to a cache of database pages, handling the I/O associated with the cache to ensure that dirty pages are written back to the file system and that new pages are allocated on demand. Applications may use the Berkeley DB shared memory buffer manager to serve their own files and pages.
Transactions and logging:
  The transaction and logging systems provide recoverability and atomicity for multiple database operations. The transaction system uses two-phase locking and write-ahead logging protocols to ensure that database operations may be undone or redone in the case of application or system failure. Applications may use Berkeley DB transaction and logging subsystems to protect their own data structures and operations from application or system failure.
Locking:
  The locking system provides multiple reader or single writer access to objects. The Berkeley DB access methods use the locking system to acquire the right to read or write database pages. Applications may use the Berkeley DB locking subsystem to support their own locking needs.

By combining the page cache, transaction, locking, and logging systems, Berkeley DB provides the same services found in much larger, more complex and more expensive database systems. Berkeley DB supports multiple simultaneous readers and writers and guarantees that all changes are recoverable, even in the case of a catastrophic hardware failure during a database update.

Developers may select some or all of the core database services for any access method or database. Therefore, it is possible to choose the appropriate storage structure and the right degrees of concurrency and recoverability for any application. In addition, some of the subsystems (for example, the Locking subsystem) can be called separately from the Berkeley DB access method. As a result, developers can integrate non-database objects into their transactional applications using Berkeley DB.

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