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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Access Methods</dl></h3></td>
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<h1 align=center>What are the available access methods?</h1>
<p>Berkeley DB currently offers four access methods: Btree, Hash, Queue and Recno.
<h3>Btree</h3>
<p>The Btree access method is an implementation of a sorted, balanced tree
structure. Searches, insertions, and deletions in the tree all take O(log
base_b N) time, where base_b is the average number of keys per page, and
N is the total number of keys stored. Often, inserting ordered data into
Btree implementations results in pages that are only half-full. Berkeley DB
makes ordered (or inverse ordered) insertion the best case, resulting in
nearly full-page space utilization.
<h3>Hash</h3>
<p>The Hash access method data structure is an implementation of Extended
Linear Hashing, as described in "Linear Hashing: A New Tool for File and
Table Addressing", Witold Litwin, <i>Proceedings of the 6th
International Conference on Very Large Databases (VLDB)</i>, 1980.
<h3>Queue</h3>
<p>The Queue access method stores fixed-length records with logical record
numbers as keys. It is designed for fast inserts at the tail and has a
special cursor consume operation that deletes and returns a record from
the head of the queue. The Queue access method uses record level locking.
<h3>Recno</h3>
<p>The Recno access method stores both fixed and variable-length records with
logical record numbers as keys, optionally backed by a flat text (byte
stream) file.
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