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A driver for Apache Cassandra 1.2+ that works exclusively with the Cassandra Query Language version 3 (CQL3) and Cassandra's binary protocol.

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/*
 * Copyright DataStax, Inc.
 *
 * Licensed 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 com.datastax.driver.core;

/**
 * The distance to a Cassandra node as assigned by a
 * {@link com.datastax.driver.core.policies.LoadBalancingPolicy} (through its {@code
 * distance} method).
 * 
 * The distance assigned to an host influences how many connections the driver
 * maintains towards this host. If for a given host the assigned {@code HostDistance}
 * is {@code LOCAL} or {@code REMOTE}, some connections will be maintained by
 * the driver to this host. More active connections will be kept to
 * {@code LOCAL} host than to a {@code REMOTE} one (and thus well behaving
 * {@code LoadBalancingPolicy} should assign a {@code REMOTE} distance only to
 * hosts that are the less often queried).
 * 
 * However, if a host is assigned the distance {@code IGNORED}, no connection
 * to that host will maintained active. In other words, {@code IGNORED} should
 * be assigned to hosts that should not be used by this driver (because they
 * are in a remote data center for instance).
 */
public enum HostDistance {
    // Note: PoolingOptions rely on the order of the enum.
    LOCAL,
    REMOTE,
    IGNORED
}