/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License, Version 1.0 only
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* (the "License"). You may not use this file except in compliance
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* with the License.
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*
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* You can obtain a copy of the license at
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* trunk/opends/resource/legal-notices/OpenDS.LICENSE
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* or https://OpenDS.dev.java.net/OpenDS.LICENSE.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at
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* trunk/opends/resource/legal-notices/OpenDS.LICENSE. If applicable,
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* add the following below this CDDL HEADER, with the fields enclosed
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* by brackets "[]" replaced with your own identifying information:
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* Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*
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*
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* Copyright 2010 Sun Microsystems, Inc.
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*/
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package org.opends.sdk;
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import java.util.Collection;
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import java.util.concurrent.ScheduledExecutorService;
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import java.util.concurrent.TimeUnit;
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/**
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* A fail-over load balancing algorithm provides fault tolerance across multiple
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* underlying connection factories.
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* <p>
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* This algorithm is typically used for load-balancing <i>between</i> data
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* centers, where there is preference to always always forward connection
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* requests to the <i>closest available</i> data center. This algorithm
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* contrasts with the {@link RoundRobinLoadBalancingAlgorithm} which is used for
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* load-balancing <i>within</i> a data center.
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* <p>
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* This algorithm selects connection factories based on the order in which they
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* were provided during construction. More specifically, an attempt to obtain a
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* connection factory will always return the <i>first operational</i> connection
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* factory in the list. Applications should, therefore, organize the connection
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* factories such that the <i>preferred</i> (usually the closest) connection
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* factories appear before those which are less preferred.
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* <p>
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* If a problem occurs that temporarily prevents connections from being obtained
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* for one of the connection factories, then this algorithm automatically
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* "fails over" to the next operational connection factory in the list. If none
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* of the connection factories are operational then a
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* {@code ConnectionException} is returned to the client.
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* <p>
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* The implementation periodically attempts to connect to failed connection
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* factories in order to determine if they have become available again.
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*
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* @see RoundRobinLoadBalancingAlgorithm
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* @see Connections#newLoadBalancer(LoadBalancingAlgorithm)
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*/
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public final class FailoverLoadBalancingAlgorithm extends
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AbstractLoadBalancingAlgorithm
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{
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/**
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* Creates a new fail-over load balancing algorithm which will monitor offline
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* connection factories every 1 second using the default scheduler.
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*
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* @param factories
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* The ordered collection of connection factories.
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*/
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public FailoverLoadBalancingAlgorithm(
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final Collection<ConnectionFactory> factories)
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{
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super(factories);
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}
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/**
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* Creates a new fail-over load balancing algorithm which will monitor offline
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* connection factories using the specified frequency using the default
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* scheduler.
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*
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* @param factories
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* The connection factories.
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* @param interval
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* The interval between attempts to poll offline factories.
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* @param unit
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* The time unit for the interval between attempts to poll offline
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* factories.
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*/
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public FailoverLoadBalancingAlgorithm(
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final Collection<ConnectionFactory> factories, final long interval,
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final TimeUnit unit)
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{
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super(factories, interval, unit);
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}
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/**
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* Creates a new fail-over load balancing algorithm which will monitor offline
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* connection factories using the specified frequency and scheduler.
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*
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* @param factories
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* The connection factories.
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* @param interval
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* The interval between attempts to poll offline factories.
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* @param unit
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* The time unit for the interval between attempts to poll offline
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* factories.
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* @param scheduler
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* The scheduler which should for periodically monitoring dead
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* connection factories to see if they are usable again.
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*/
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public FailoverLoadBalancingAlgorithm(
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final Collection<ConnectionFactory> factories, final long interval,
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final TimeUnit unit, final ScheduledExecutorService scheduler)
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{
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super(factories, interval, unit, scheduler);
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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String getAlgorithmName()
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{
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return "Failover";
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}
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/**
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* {@inheritDoc}
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*/
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@Override
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int getInitialConnectionFactoryIndex()
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{
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// Always start with the first connection factory.
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return 0;
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}
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}
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