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<title>Chapter 2. Access Method Configuration</title>
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<th colspan="3" align="center">Chapter 2.
Access Method Configuration
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<div class="chapter" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title"><a id="am_conf"></a>Chapter 2.
Access Method Configuration
</h2>
</div>
</div>
</div>
<div class="toc">
<p>
<b>Table of Contents</b>
</p>
<dl>
<dt>
<span class="sect1">
<a href="am_conf.html#am_conf_intro">What are the available access methods?</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="am_conf.html#id1588967">Btree</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf.html#id1587613">Hash</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf.html#id1588266">Queue</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf.html#id1589081">Recno</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="am_conf_select.html">Selecting an access method</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="am_conf_select.html#id1589084">Hash or Btree?</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf_select.html#id1589088">Queue or Recno?</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="am_conf_logrec.html">Logical record numbers</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="general_am_conf.html">General access method configuration</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="general_am_conf.html#am_conf_pagesize">Selecting a page size</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="general_am_conf.html#am_conf_cachesize">Selecting a cache size</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="general_am_conf.html#am_conf_byteorder">Selecting a byte order</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="general_am_conf.html#am_conf_dup">Duplicate data items</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="general_am_conf.html#am_conf_malloc">Non-local memory allocation</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="bt_conf.html">Btree access method specific configuration</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="bt_conf.html#am_conf_bt_compare">Btree comparison</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="bt_conf.html#am_conf_bt_prefix">Btree prefix comparison</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="bt_conf.html#am_conf_bt_minkey">Minimum keys per page</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="bt_conf.html#am_conf_bt_recnum">Retrieving Btree records by logical record number</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="bt_conf.html#am_conf_bt_compress">Compression</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="hash_conf.html">Hash access method specific configuration</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="hash_conf.html#am_conf_h_ffactor">Page fill factor</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="hash_conf.html#am_conf_h_hash">Specifying a database hash</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="hash_conf.html#am_conf_h_nelem">Hash table size</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="rq_conf.html">Queue and Recno access method specific configuration</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="rq_conf.html#am_conf_recno">Managing record-based databases</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="rq_conf.html#am_conf_extentsize">Selecting a Queue extent size</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="rq_conf.html#am_conf_re_source">Flat-text backing files</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="rq_conf.html#am_conf_renumber">Logically renumbering records</a>
</span>
</dt>
</dl>
</dd>
</dl>
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="am_conf_intro"></a>What are the available access methods?</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="am_conf.html#id1588967">Btree</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf.html#id1587613">Hash</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf.html#id1588266">Queue</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_conf.html#id1589081">Recno</a>
</span>
</dt>
</dl>
</div>
<p>Berkeley DB currently offers four access methods: Btree, Hash, Queue and Recno.</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1588967"></a>Btree</h3>
</div>
</div>
</div>
<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.</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1587613"></a>Hash</h3>
</div>
</div>
</div>
<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, <span class="emphasis"><em>Proceedings of the 6th
International Conference on Very Large Databases (VLDB)</em></span>, 1980.</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1588266"></a>Queue</h3>
</div>
</div>
</div>
<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.</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="id1589081"></a>Recno</h3>
</div>
</div>
</div>
<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.</p>
</div>
</div>
</div>
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<td width="40%" align="right"> <a accesskey="n" href="am_conf_select.html">Next</a></td>
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<tr>
<td width="40%" align="left" valign="top">The Berkeley DB products </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Selecting an access method</td>
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