com.datastax.driver.core.HostDistance Maven / Gradle / Ivy

/*
 * 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
}