com.datastax.oss.driver.api.core.loadbalancing

Interface NodeDistanceEvaluator

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface
public interface NodeDistanceEvaluator

A pluggable NodeDistance evaluator.

Node distance evaluators are recognized by all the driver built-in load balancing policies. They can be specified programmatically or through the configuration (with the load-balancing-policy.evaluator.class option).

See Also:

SessionBuilder.withNodeDistanceEvaluator(String, NodeDistanceEvaluator)

Method Summary

Modifier and Type	Method and Description
NodeDistance	evaluateDistance(Node node, String localDc) Evaluates the distance to apply to the given node.

Method Detail

evaluateDistance

@Nullable
NodeDistance evaluateDistance(@NonNull
                                        Node node,
                                        @Nullable
                                        String localDc)

Evaluates the distance to apply to the given node.

This method will be invoked each time the 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 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.

Parameters:

node - The node to assign a new distance to.

localDc - The local datacenter name, if defined, or null otherwise.

Returns:

The NodeDistance to assign to the node, or null to let the policy decide.