org.apache.avalon.excalibur.datasource.cluster.DefaultRoundRobinDataSourceCluster Maven / Gradle / Ivy

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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed  under the  License is distributed on an "AS IS" BASIS,
 * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
 * implied.
 * 
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.avalon.excalibur.datasource.cluster;

import java.sql.Connection;
import java.sql.SQLException;

/**
 * The DefaultRoundRobinDataSourceCluster allows the user to specify a cluster of DataSources
 *  which all act as one.  The Cluster works by cycling through its member DataSources returning
 *  a connection from a different one with each call to getConnection().
 * 
 * This form of Clustering has the benefit that it can be used by components without requiring
 *  any changes.  But care must be taken as to the kind of data written or read from the database.
 *  Wich this clustering method, there is no control over which DataSource will provide a
 *  connection for any given call.
 * 

 * Round Robin Clusters are useful in cases where lots of read-only data needs to be accessed and
 *  multiple copies of the data can be stored on different database servers to balance load.
 * 

 * The Configuration for a 2 database cluster is like this:
 *
 * 
 *   <datasources>
 *     <roundrobin-cluster name="mydb-cluster" size="2">
 *       <dbpool index="0">mydb-0</dbpool>
 *       <dbpool index="1">mydb-1</dbpool>
 *     </roundrobin-cluster>
 *   </datasources>
 *   <cluster-datasources>
 *     <jdbc name="mydb-0">
 *       <pool-controller min="1" max="10"/>
 *       <auto-commit>true</auto-commit>
 *       <driver>com.database.jdbc.JdbcDriver</driver>
 *       <dburl>jdbc:driver://host0/mydb</dburl>
 *       <user>username</user>
 *       <password>password</password>
 *     </jdbc>
 *     <jdbc name="mydb-1">
 *       <pool-controller min="1" max="10"/>
 *       <auto-commit>true</auto-commit>
 *       <driver>com.database.jdbc.JdbcDriver</driver>
 *       <dburl>jdbc:driver://host1/mydb</dburl>
 *       <user>username</user>
 *       <password>password</password>
 *     </jdbc>
 *   </cluster-datasources>
 * 
 *
 * With the following roles declaration:
 *
 *  *   <role name="org.apache.avalon.excalibur.datasource.DataSourceComponentSelector"
 *       shorthand="datasources"
 *       default-class="org.apache.avalon.excalibur.component.ExcaliburComponentSelector">
 *     <hint shorthand="jdbc" class="org.apache.avalon.excalibur.datasource.JdbcDataSource"/>
 *     <hint shorthand="j2ee" class="org.apache.avalon.excalibur.datasource.J2eeDataSource"/>
 *     <hint shorthand="roundrobin-cluster"
 *         class="org.apache.avalon.excalibur.datasource.cluster.DefaultRoundRobinDataSourceCluster"/>
 *   </role>
 *   <role name="org.apache.avalon.excalibur.datasource.DataSourceComponentClusterSelector"
 *       shorthand="cluster-datasources"
 *       default-class="org.apache.avalon.excalibur.component.ExcaliburComponentSelector">
 *     <hint shorthand="jdbc" class="org.apache.avalon.excalibur.datasource.JdbcDataSource"/>
 *     <hint shorthand="j2ee" class="org.apache.avalon.excalibur.datasource.J2eeDataSource"/>
 *   </role>
 * 
 * 
 * @avalon.component
 * @avalon.service type=org.apache.avalon.excalibur.datasource.DataSourceComponent
 * @avalon.service type=RoundRobinDataSourceCluster
 * @x-avalon.info name=rrobin-db-cluster
 * @x-avalon.lifestyle type=singleton
 *
 * @author Avalon Development Team
 * @version CVS $Revision: 1.4 $ $Date: 2004/02/28 11:47:20 $
 * @since 4.1
 */
public class DefaultRoundRobinDataSourceCluster
    extends AbstractDataSourceCluster
    implements RoundRobinDataSourceCluster
{
    private Object m_semaphore = new Object();
    private int m_nextIndex;

    /*---------------------------------------------------------------
     * Constructors
     *-------------------------------------------------------------*/
    public DefaultRoundRobinDataSourceCluster()
    {
    }

    /*---------------------------------------------------------------
     * DataSourceComponent Methods
     *-------------------------------------------------------------*/
    /**
     * Returns a Connection to one of the Cluster's member DataSources.
     *
     * @throws NoValidConnectionException when there is no valid Connection wrapper
     *         available in the classloader.
     *
     * @throws NoValidConnectionException when there are no more available
     *         Connections in the pool.
     */
    public Connection getConnection() throws SQLException
    {
        int index;
        synchronized( m_semaphore )
        {
            index = m_nextIndex;
            if( ( ++m_nextIndex ) >= m_size )
            {
                m_nextIndex = 0;
            }
        }

        return getConnectionForIndex( index );
    }
}