View Source Xandra.Cluster.LoadBalancingPolicy behaviour (Xandra v0.19.1)

A behaviour for defining load-balancing policies.

A load-balancing policy is a way to tell Xandra which nodes to query when connected to a cluster.

For example, a simple load-balancing policy is Xandra.Cluster.LoadBalancingPolicy.Random, which picks a random node for each query out of the ones that are up.

Summary

Types

state()

The state of the load-balancing policy.

Callbacks

host_added(state, host)

Called when the Cassandra cluster reports a new host that joined.

host_connected(state, host)

Called when Xandra successfully connects to host.

host_down(state, host)

Called when the Cassandra cluster marks host as "down".

host_removed(state, host)

Called when the Cassandra cluster reports a host that left the cluster.

host_up(state, host)

Called when the Cassandra gossip marks host as "up".

hosts_plan(state)

Called to return a "plan", which is an enumerable of hosts to start connections in order.

init(options)

Called to initialize the load-balancing policy.

query_plan(state)

Called to return a "plan", which is an enumerable of hosts to query in order.

Types

state()

(since 0.15.0)

@type state() :: term()

The state of the load-balancing policy.

Can be any term and is passed around to all callbacks.

Callbacks

host_added(state, host)

(since 0.15.0)

@callback host_added(state(), host :: Xandra.Cluster.Host.t()) :: state()

Called when the Cassandra cluster reports a new host that joined.

host_connected(state, host)

(since 0.15.0)

@callback host_connected(state(), host :: Xandra.Cluster.Host.t()) :: state()

Called when Xandra successfully connects to host.

host_down(state, host)

(since 0.15.0)

@callback host_down(state(), host :: Xandra.Cluster.Host.t()) :: state()

Called when the Cassandra cluster marks host as "down".

host_removed(state, host)

(since 0.15.0)

@callback host_removed(state(), host :: Xandra.Cluster.Host.t()) :: state()

Called when the Cassandra cluster reports a host that left the cluster.

host_up(state, host)

(since 0.15.0)

@callback host_up(state(), host :: Xandra.Cluster.Host.t()) :: state()

Called when the Cassandra gossip marks host as "up".

hosts_plan(state)

(since 0.15.0)

@callback hosts_plan(state()) :: {Enumerable.t(Xandra.Cluster.Host.t()), state()}

Called to return a "plan", which is an enumerable of hosts to start connections in order.

init(options)

(since 0.15.0)

@callback init(options :: term()) :: state()

Called to initialize the load-balancing policy.

options is given by the user when configuring the cluster, and is specific to the load-balancing policy.

query_plan(state)

(since 0.15.0)

@callback query_plan(state()) :: {Enumerable.t(Xandra.Cluster.Host.t()), state()}

Called to return a "plan", which is an enumerable of hosts to query in order.