2011-09-13 17:44:24 +00:00
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<title>DB->set_partition()</title>
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<link rel="start" href="index.html" title="Berkeley DB C API Reference" />
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<link rel="up" href="db.html" title="Chapter 2. The DB Handle" />
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<link rel="prev" href="dbset_pagesize.html" title="DB->set_pagesize()" />
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<link rel="next" href="dbset_partition_dirs.html" title="DB->set_partition_dirs()" />
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<div class="libver">
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2012-11-14 21:35:20 +00:00
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<p>Library Version 11.2.5.3</p>
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2011-09-13 17:44:24 +00:00
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">DB->set_partition()</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="dbset_pagesize.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 2.
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The DB Handle
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</th>
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<td width="20%" align="right"> <a accesskey="n" href="dbset_partition_dirs.html">Next</a></td>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="dbset_partition"></a>DB->set_partition()</h2>
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</div>
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</div>
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</div>
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<pre class="programlisting">#include <db.h>
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int
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DB->set_partition(DB * db, u_int32_t parts, DBT *keys,
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u_int32_t (*db_partition_fcn) (DB *db, DBT *key)); </pre>
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<p>
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Set up partitioning for a database. Partitioning may be used on either BTREE or HASH databases.
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Partitions may be specified by either a set of keys specifying a range of values in each partition
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or with a callback function that returns the number of the partition to put a specific key.
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Partition range keys may only be specified for BTREE databases.
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</p>
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<p>
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Partitions are implimented as separate database files and can help reduce contention within a logical
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database. Contention can come from multiple threads of control accessing database pages simultaniously.
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Typically these pages are the root of a btree and the metadata page which contains allocation information
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in both BTREE and HASH databases. Each partition has its own metadata and root pages.
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</p>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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2012-11-14 21:35:20 +00:00
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<h3 class="title"><a id="idp58470008"></a>Parameters</h3>
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2011-09-13 17:44:24 +00:00
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</div>
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<p>
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Exactly one of the parameters
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<span class="bold"><strong>keys</strong></span> and
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<span class="bold"><strong>partition_fcn</strong></span> must be NULL.
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</p>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp58489904"></a>parts</h4>
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>parts</strong></span> parameter is the number of partitions to create.
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The value must be 2 or greater.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h4 class="title"><a id="idp58458096"></a>keys</h4>
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2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>keys</strong></span> parameter is an
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array of DBT structures containing the keys that specify
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the range of key values to be stored in each partition.
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Each key specifies the minimum value that may be stored in
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the corresponding partition. The number of keys must be
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one less than the number of partitions specified by the
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<span class="bold"><strong>parts</strong></span> parameter since the
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first partition will hold any key less than the first key
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in the array.
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</p>
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</div>
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<div class="sect3" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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2012-11-14 21:35:20 +00:00
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<h4 class="title"><a id="idp58480440"></a>db_partition_fcn</h4>
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2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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The <span class="bold"><strong>db_partition_fcn</strong></span>
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parameter is the application-specified partitioning
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function. The function returns an integer which will be
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used modulo the number of partitions specified by the
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<span class="bold"><strong>parts</strong></span> parameter.
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The function will be called with two parameters:
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</p>
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<div class="itemizedlist">
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<ul type="disc">
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<li>
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<p>
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<code class="literal">db</code>
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</p>
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<p>
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The <span class="bold"><strong>db</strong></span> parameter is the database handle.
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</p>
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</li>
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<li>
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<p>
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<code class="literal">key</code>
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</p>
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<p>
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The <span class="bold"><strong>key</strong></span> parameter
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is the key for which a partition number should be
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returned.
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</p>
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</li>
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</ul>
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</div>
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</div>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h3 class="title"><a id="idp58494264"></a>Class</h3>
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2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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<a class="link" href="db.html" title="Chapter 2. The DB Handle">DB</a>
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</p>
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</div>
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<div class="sect2" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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2012-11-14 21:35:20 +00:00
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<h3 class="title"><a id="idp58488664"></a>See Also</h3>
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2011-09-13 17:44:24 +00:00
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</div>
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</div>
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</div>
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<p>
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<a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a>
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</p>
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<td width="40%" align="left"><a accesskey="p" href="dbset_pagesize.html">Prev</a> </td>
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<a accesskey="u" href="db.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="dbset_partition_dirs.html">Next</a></td>
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<td width="40%" align="left" valign="top">DB->set_pagesize() </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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<td width="40%" align="right" valign="top"> DB->set_partition_dirs()</td>
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</tr>
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