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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<title>Chapter 3. Access Method Operations</title>
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<body>
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Chapter 3.
Access Method Operations
</th>
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</tr>
</table>
<hr />
</div>
<div class="chapter" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title"><a id="am"></a>Chapter 3.
Access Method Operations
</h2>
</div>
</div>
</div>
<div class="toc">
<p>
<b>Table of Contents</b>
</p>
<dl>
<dt>
<span class="sect1">
<a href="am.html#am_open">Database open</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_opensub.html">Opening multiple databases in a single file</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="am_opensub.html#idp50593360">Configuring databases sharing a file</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_opensub.html#idp50628832">Caching databases sharing a file</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_opensub.html#idp50629528">Locking in databases based on sharing a file</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="am_partition.html">Partitioning databases</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="am_partition.html#am_partition_keys">Specifying partition keys</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_partition.html#am_partition_function">Partitioning callback</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_partition.html#partition_file_placement">Placing partition files</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="am_get.html">Retrieving records</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_put.html">Storing records</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_delete.html">Deleting records</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_stat.html">Database statistics</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_truncate.html">Database truncation</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_upgrade.html">Database upgrade</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_verify.html">Database verification and salvage</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_sync.html">Flushing the database cache</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_close.html">Database close</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_second.html">Secondary indexes</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="am_second.html#idp50703760">Error Handling With Secondary Indexes</a>
</span>
</dt>
</dl>
</dd>
<dt>
<span class="sect1">
<a href="am_foreign.html">Foreign key indexes</a>
</span>
</dt>
<dt>
<span class="sect1">
<a href="am_cursor.html">Cursor operations</a>
</span>
</dt>
<dd>
<dl>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_curget">Retrieving records with a cursor</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_curput">Storing records with a cursor</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_curdel">Deleting records with a cursor</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_curdup">Duplicating a cursor</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_join">Equality Join</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_count">Data item count</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="am_cursor.html#am_curclose">Cursor close</a>
</span>
</dt>
</dl>
</dd>
</dl>
</div>
<p>Once a database handle has been created using <a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a>, there
are several standard access method operations. Each of these operations
is performed using a method referred to by the returned handle.
Generally, the database will be opened using <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a>. If the
database is from an old release of Berkeley DB, it may need to be upgraded to
the current release before it is opened using <a href="../api_reference/C/dbupgrade.html" class="olink">DB->upgrade()</a>.</p>
<p>Once a database has been opened, records may be retrieved (<a href="../api_reference/C/dbget.html" class="olink">DB->get()</a>),
stored (<a href="../api_reference/C/dbput.html" class="olink">DB->put()</a>), and deleted (<a href="../api_reference/C/dbdel.html" class="olink">DB->del()</a>).</p>
<p>Additional operations supported by the database handle include
statistics (<a href="../api_reference/C/dbstat.html" class="olink">DB->stat()</a>), truncation (<a href="../api_reference/C/dbtruncate.html" class="olink">DB->truncate()</a>),
version upgrade (<a href="../api_reference/C/dbupgrade.html" class="olink">DB->upgrade()</a>), verification and salvage
(<a href="../api_reference/C/dbverify.html" class="olink">DB->verify()</a>), flushing to a backing file (<a href="../api_reference/C/dbsync.html" class="olink">DB->sync()</a>),
and association of secondary indices (<a href="../api_reference/C/dbassociate.html" class="olink">DB->associate()</a>). Database
handles are eventually closed using <a href="../api_reference/C/dbclose.html" class="olink">DB->close()</a>.</p>
<div class="informaltable">
<table border="1" width="80%">
<colgroup>
<col />
<col />
</colgroup>
<thead>
<tr>
<th>Database Operations</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>
<a href="../api_reference/C/dbcreate.html" class="olink">db_create()</a>
</td>
<td>Create a database handle</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbassociate.html" class="olink">DB->associate()</a>
</td>
<td>Associate a secondary index</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbassociate_foreign.html" class="olink">DB->associate_foreign()</a>
</td>
<td>Associate a foreign index</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbclose.html" class="olink">DB->close()</a>
</td>
<td>Close a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbcompact.html" class="olink">DB->compact()</a>
</td>
<td>Compact a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbcursor.html" class="olink">DB->cursor()</a>
</td>
<td>Create a cursor</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbdel.html" class="olink">DB->del()</a>
</td>
<td>Delete items from a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dberr.html" class="olink">DB->err()</a>
</td>
<td>Error message</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbexists.html" class="olink">DB->existis()</a>
</td>
<td>Return if an item appears in a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbfd.html" class="olink">DB->fd()</a>
</td>
<td>Return a file descriptor from a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbget.html" class="olink">DB->get()</a>
</td>
<td>Get items from a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbget_byteswapped.html" class="olink">DB->get_byteswapped()</a>
</td>
<td>Return if the underlying database is in host order</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbget_type.html" class="olink">DB->get_type()</a>
</td>
<td>Return the database type</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbjoin.html" class="olink">DB->join()</a>
</td>
<td>Perform a database join on cursors</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbkey_range.html" class="olink">DB->key_range()</a>
</td>
<td>Return estimate of key location</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a>
</td>
<td>Open a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbput.html" class="olink">DB->put()</a>
</td>
<td>Store items into a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbremove.html" class="olink">DB->remove()</a>
</td>
<td>Remove a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbrename.html" class="olink">DB->rename()</a>
</td>
<td>Rename a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_priority.html" class="olink">DB->set_priority()</a>
</td>
<td>Set cache page priority</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbstat.html" class="olink">DB->stat()</a>
</td>
<td>Database statistics</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbsync.html" class="olink">DB->sync()</a>
</td>
<td>Flush a database to stable storage</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbtruncate.html" class="olink">DB->truncate()</a>
</td>
<td>Empty a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbupgrade.html" class="olink">DB->upgrade()</a>
</td>
<td>Upgrade a database</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbverify.html" class="olink">DB->verify()</a>
</td>
<td>Verify/salvage a database</td>
</tr>
<tr>
<td>Database Configuration</td>
<td> </td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_alloc.html" class="olink">DB->set_alloc()</a>
</td>
<td>Set local space allocation functions</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a>
</td>
<td>Set the database cache size</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_dup_compare.html" class="olink">DB->set_dup_compare()</a>
</td>
<td>Set a duplicate comparison function</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_encrypt.html" class="olink">DB->set_encrypt()</a>
</td>
<td>Set the database cryptographic key</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_errcall.html" class="olink">DB->set_errcall()</a>
</td>
<td>Set error and informational message callback</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_errfile.html" class="olink">DB->set_errfile()</a>
</td>
<td>Set error and informational message FILE</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_errpfx.html" class="olink">DB->set_errpfx()</a>
</td>
<td>Set error message prefix</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_feedback.html" class="olink">DB->set_feedback()</a>
</td>
<td>Set feedback callback</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_flags.html" class="olink">DB->set_flags()</a>
</td>
<td>General database configuration</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_lorder.html" class="olink">DB->set_lorder()</a>
</td>
<td>Set the database byte order</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_pagesize.html" class="olink">DB->set_pagesize()</a>
</td>
<td>Set the underlying database page size</td>
</tr>
<tr>
<td>Btree/Recno Configuration</td>
<td> </td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_append_recno.html" class="olink">DB->set_append_recno()</a>
</td>
<td>Set record append callback</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_bt_compare.html" class="olink">DB->set_bt_compare()</a>
</td>
<td>Set a Btree comparison function</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_bt_minkey.html" class="olink">DB->set_bt_minkey()</a>
</td>
<td>Set the minimum number of keys per Btree page</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_bt_prefix.html" class="olink">DB->set_bt_prefix()</a>
</td>
<td>Set a Btree prefix comparison function</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_re_delim.html" class="olink">DB->set_re_delim()</a>
</td>
<td>Set the variable-length record delimiter</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_re_len.html" class="olink">DB->set_re_len()</a>
</td>
<td>Set the fixed-length record length</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_re_pad.html" class="olink">DB->set_re_pad()</a>
</td>
<td>Set the fixed-length record pad byte</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_re_source.html" class="olink">DB->set_re_source()</a>
</td>
<td>Set the backing Recno text file</td>
</tr>
<tr>
<td>Hash Configuration</td>
<td> </td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_h_compare.html" class="olink">DB->set_h_compare()</a>
</td>
<td>Set a Hash comparison function</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_h_ffactor.html" class="olink">DB->set_h_ffactor()</a>
</td>
<td>Set the Hash table density</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_h_hash.html" class="olink">DB->set_h_hash()</a>
</td>
<td>Set a hashing function</td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_h_nelem.html" class="olink">DB->set_h_nelem()</a>
</td>
<td>Set the Hash table size</td>
</tr>
<tr>
<td>Queue Configuration</td>
<td> </td>
</tr>
<tr>
<td>
<a href="../api_reference/C/dbset_q_extentsize.html" class="olink">DB->set_q_extentsize()</a>
</td>
<td>Set Queue database extent size</td>
</tr>
</tbody>
</table>
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="am_open"></a>Database open</h2>
</div>
</div>
</div>
<p>The <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a> method opens a database, and takes five arguments:</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">file</span>
</dt>
<dd>The name of the file to be opened.</dd>
<dt>
<span class="term">database</span>
</dt>
<dd>An optional database name.</dd>
<dt>
<span class="term">type</span>
</dt>
<dd>The type of database to open. This value will be one of the four access
methods Berkeley DB supports: DB_BTREE, DB_HASH, DB_QUEUE or DB_RECNO, or the
special value DB_UNKNOWN, which allows you to open an existing file
without knowing its type.</dd>
<dt>
<span class="term">mode</span>
</dt>
<dd>The permissions to give to any created file.</dd>
</dl>
</div>
<p>There are a few flags that you can set to customize open:</p>
<div class="variablelist">
<dl>
<dt>
<span class="term">
<a href="../api_reference/C/dbopen.html#open_DB_CREATE" class="olink">DB_CREATE</a>
</span>
</dt>
<dd>Create the underlying database and any necessary physical files.</dd>
<dt>
<span class="term">
<a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a>
</span>
</dt>
<dd>Do not map this database into process memory.</dd>
<dt>
<span class="term">
<a href="../api_reference/C/dbopen.html#dbopen_DB_RDONLY" class="olink">DB_RDONLY</a>
</span>
</dt>
<dd>Treat the data base as read-only.</dd>
<dt>
<span class="term">
<a href="../api_reference/C/dbopen.html#open_DB_THREAD" class="olink">DB_THREAD</a>
</span>
</dt>
<dd>The returned handle is free-threaded, that is, it can be used
simultaneously by multiple threads within the process.</dd>
<dt>
<span class="term">
<a href="../api_reference/C/dbopen.html#open_DB_TRUNCATE" class="olink">DB_TRUNCATE</a>
</span>
</dt>
<dd>Physically truncate the underlying database file, discarding all
databases it contained. Underlying filesystem primitives are used to
implement this flag. For this reason it is only applicable to the
physical file and cannot be used to discard individual databases from
within physical files.</dd>
<dt>
<span class="term">
<a href="../api_reference/C/dbset_feedback.html#set_feedback_DB_UPGRADE" class="olink">DB_UPGRADE</a>
</span>
</dt>
<dd>Upgrade the database format as necessary.</dd>
</dl>
</div>
</div>
</div>
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