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<h2 class="title" style="clear: both"><a id="dbset_partition"></a>Db::set_partition()</h2>
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<pre class="programlisting">#include <db_cxx.h>
int
Db::set_partition(u_int32_t parts, DBT *kyes,
u_int32_t (*db_partition_fcn) (Db *db, DBT *key));</pre>
<p>
Set up partitioning for a database. Partitioning may be used on
either BTREE or HASH databases. Partitions may be specified by
either a set of keys specifying a range of values in each
partition, or with a callback function that returns the number of
the partition to put a specific key. Partition range keys may only
be specified for BTREE databases.
</p>
<p>
Partitions are implemented as separate database files and can help
reduce contention within a logical database. Contention can come
from multiple threads of control accessing database pages
simultaneously. Typically these pages are the root of a btree and
the metadata page which contains allocation information in both
BTREE and HASH databases. Each partition has its own metadata and
root pages.
</p>
<div class="sect2" lang="en" xml:lang="en">
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<div>
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<h3 class="title"><a id="idp361288"></a>Parameters</h3>
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<p>
Exactly one of the parameters
<span class="bold"><strong>keys</strong></span> and
<span class="bold"><strong>partition_fcn</strong></span> must be NULL.
</p>
<div class="sect3" lang="en" xml:lang="en">
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<div>
<div>
<h4 class="title"><a id="idp370432"></a>parts</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>parts</strong></span> parameter is the
number of partitions to create. The value must be greater than
or equal to 2, and smaller than 1000000.
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<div class="sect3" lang="en" xml:lang="en">
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<h4 class="title"><a id="idp356216"></a>keys</h4>
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<p>
The <span class="bold"><strong>keys</strong></span> parameter is an
array of DBT structures containing the keys that specify
the range of key values to be stored in each partition.
Each key specifies the minimum value that may be stored in
the corresponding partition. The number of keys must be
one less than the number of partitions specified by the
<span class="bold"><strong>parts</strong></span> parameter since the
first partition will hold any key less than the first key
in the array.
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<div class="sect3" lang="en" xml:lang="en">
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<h4 class="title"><a id="idp323328"></a>db_partition_fcn</h4>
</div>
</div>
</div>
<p>
The <span class="bold"><strong>db_partition_fcn</strong></span>
parameter is the application-specified partitioning
function. The function returns an integer which will be
used modulo the number of partitions specified by the
<span class="bold"><strong>parts</strong></span> parameter.
The function will be called with two parameters:
</p>
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<code class="literal">db</code>
</p>
<p>
The <span class="bold"><strong>db</strong></span> parameter
is the database handle.
</p>
</li>
<li>
<p>
<code class="literal">key</code>
</p>
<p>
The <span class="bold"><strong>key</strong></span> parameter
is the key for which a partition number should be
returned.
</p>
</li>
</ul>
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<a class="link" href="db.html" title="Chapter 2. The Db Handle">Db</a>
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<h3 class="title"><a id="idp357376"></a>See Also</h3>
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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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