bdb.rd

# BDB

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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.

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With bdb >= 0.5.5 nil is stored as an empty string (when marshal is not used).

Open the database with

    "store_nil_as_null" => true

if you want the old behavior (nil stored as `\000')

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The library includes support for the following access methods:

- B+tree: Stores keys in sorted order, using a default function that does lexicographical ordering of keys.
- Hashing: Stores records in a hash table for fast searches based on strict equality, using a default that hashes on the key as a bit string. Extended Linear Hashing modifies the hash function used by the table as new records are inserted, in order to keep buckets underfull in the steady state.
- Fixed and Variable-Length Records: Stores fixed- or variable-length records in sequential order. Record numbers may be immutable, requiring that new records be added only at the end of the database, or mutable, permitting new records to be inserted between existing records.

Berkeley DB environnement

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.

Acces Methods

- Hash like interface these are the common methods for BDB::Btree, BDB::Hash, BDB::Recno, BDB::Queue
- Array like interface methods for BDB::Recnum

Sequence

A sequence is created with BDB::Common::create_sequence or BDB::Common::open_sequence (only with db >= 4.3)

Transaction Manager

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.

Cursor operation

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

Lock system

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.

Logging subsystem

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.