com.datastax.oss.driver.api.core.loadbalancing.NodeDistanceEvaluator Maven / Gradle / Ivy
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* 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
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*/
package com.datastax.oss.driver.api.core.loadbalancing;
import com.datastax.oss.driver.api.core.metadata.Node;
import edu.umd.cs.findbugs.annotations.NonNull;
import edu.umd.cs.findbugs.annotations.Nullable;
/**
* A pluggable {@link NodeDistance} evaluator.
*
* Node distance evaluators are recognized by all the driver built-in load balancing policies.
* They can be specified {@linkplain
* com.datastax.oss.driver.api.core.session.SessionBuilder#withNodeDistanceEvaluator(String,
* NodeDistanceEvaluator) programmatically} or through the configuration (with the {@code
* load-balancing-policy.evaluator.class} option).
*
* @see com.datastax.oss.driver.api.core.session.SessionBuilder#withNodeDistanceEvaluator(String,
* NodeDistanceEvaluator)
*/
@FunctionalInterface
public interface NodeDistanceEvaluator {
/**
* Evaluates the distance to apply to the given node.
*
*
This method will be invoked each time the {@link LoadBalancingPolicy} processes a topology
* or state change, and will be passed the node being inspected, and the local datacenter name (or
* null if none is defined). If it returns a non-null {@link NodeDistance}, the policy will
* suggest that distance for the node; if it returns null, the policy will assign a default
* distance instead, based on its internal algorithm for computing node distances.
*
* @param node The node to assign a new distance to.
* @param localDc The local datacenter name, if defined, or null otherwise.
* @return The {@link NodeDistance} to assign to the node, or null to let the policy decide.
*/
@Nullable
NodeDistance evaluateDistance(@NonNull Node node, @Nullable String localDc);
}