Class: DefaultLoadBalancingPolicy

policies/loadBalancing~DefaultLoadBalancingPolicy(optionsopt)

A load-balancing policy implementation that attempts to fairly distribute the load based on the amount of in-flight request per hosts. The local replicas are initially shuffled and between the first two nodes in the shuffled list, the one with fewer in-flight requests is selected as coordinator.

Additionally, it detects unresponsive replicas and reorders them at the back of the query plan.

For graph analytics queries, it uses the preferred analytics graph server previously obtained by driver as first host in the query plan.

Constructor

new DefaultLoadBalancingPolicy(optionsopt)

Creates a new instance of DefaultLoadBalancingPolicy.

Parameters:
Name Type Attributes Description
options String | Object <optional>

The local data center name or the optional policy options object.

Note that when providing the local data center name, it overrides localDataCenter option at Client level.

Properties
Name Type Attributes Description
localDc String <optional>

local data center name. This value overrides the 'localDataCenter' Client option and is useful for cases where you have multiple execution profiles that you intend on using for routing requests to different data centers.
filter function <optional>

A function to apply to determine if hosts are included in the query plan. The function takes a Host parameter and returns a Boolean.
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Methods

getDistance(host)

Returns the distance assigned by this policy to the provided host, relatively to the client instance.

Parameters:
Name Type Description
host Host
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getOptions()

Gets an associative array containing the policy options.

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init(client, hosts, callback)

Initializes the load balancing policy, called after the driver obtained the information of the cluster.

Parameters:
Name Type Description
client Client
hosts HostMap
callback function
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newQueryPlan(keyspace, executionOptions, callback)

Returns a host iterator to be used for a query execution.

Parameters:
Name Type Description
keyspace String
executionOptions ExecutionOptions
callback function
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(generator) yieldReplicasFirst(replicas)

Yields the local replicas followed by the rest of local nodes.

Parameters:
Name Type Description
replicas Array.<Host>

The local replicas
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