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<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">About Clustered Databases and Oracle RAC</font></h1>
<p>Some databases support clustering the database across multiple machines. Oracle RAC allows for a single database to span multiple different server nodes. Oracle RAC also supports table and node partitioning of data. A database cluster allows for any of the data to be accessed from any node in the cluster. However, it is generally more efficient to partition the data access to specific nodes, to reduce cross node communication.</p>
<p>EclipseLink partitioning can be used in conjunction with a clustered database to reduce cross node communication, and improve scalability.</p>
<p>To use partitioning with a database cluster to following is required:</p>
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<li>
<p>The partition policy should not enable replication, as the database cluster makes data available to all nodes.</p>
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<p>The partition policy should not use unions, as the database cluster returns the complete query result from any node.</p>
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<li>
<p>A data source and EclipseLink connection pool should be defined for each node in the cluster.</p>
</li>
<li>
<p>The application's data access and data partitioning should be designed to have each transaction only require access to a single node.</p>
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<p>Use of an exclusive connection for an EntityManager is recommended to avoid having multiple nodes in a single transaction and avoid 2-phase commit.</p>
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