Class: Cassandra::LoadBalancing::Policies::TokenAware

Inherits:
Cassandra::LoadBalancing::Policy show all
Extended by:
Forwardable
Defined in:
lib/cassandra/load_balancing/policies/token_aware.rb

Instance Method Summary collapse

Constructor Details

#initialize(wrapped_policy, shuffle = true) ⇒ TokenAware

Note:

If replicas are not shuffled (shuffle = false), then it is possibile to create hotspots in a write-heavy scenario, where most of the write requests will be handled by the same node(s). The default behavior of shuffling replicas helps mitigate this by universally distributing write load between replicas. However, it under-utilizes read caching and forces multiple replicas to cache the same read statements.

Returns a new instance of TokenAware.

Parameters:

  • wrapped_policy (Cassandra::LoadBalancing::Policy) —

    actual policy to filter

  • shuffle (Boolean) (defaults to: true) —

    (true) whether or not to shuffle the replicas



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 101

def initialize(wrapped_policy, shuffle = true)
  methods = [:host_up, :host_down, :host_found, :host_lost, :setup, :teardown,
             :distance, :plan]

  Util.assert_responds_to_all(methods, wrapped_policy) do
    "supplied policy must respond to #{methods.inspect}, but doesn't"
  end

  @policy  = wrapped_policy
  @shuffle = !!shuffle
end

Instance Method Details

#distance(host) ⇒ Object

Delegates to wrapped policy

See Also:



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 88

def_delegators :@policy, :distance, :host_found, :host_up, :host_down, :host_lost

#host_down(host) ⇒ Object

Delegates to wrapped policy

See Also:



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 88

def_delegators :@policy, :distance, :host_found, :host_up, :host_down, :host_lost

#host_found(host) ⇒ Object

Delegates to wrapped policy

See Also:



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 88

def_delegators :@policy, :distance, :host_found, :host_up, :host_down, :host_lost

#host_lost(host) ⇒ Object

Delegates to wrapped policy

See Also:



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 88

def_delegators :@policy, :distance, :host_found, :host_up, :host_down, :host_lost

#host_up(host) ⇒ Object

Delegates to wrapped policy

See Also:



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 88

def_delegators :@policy, :distance, :host_found, :host_up, :host_down, :host_lost

#plan(keyspace, statement, options) ⇒ Object 



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 125

def plan(keyspace, statement, options)
  return @policy.plan(keyspace, statement, options) unless @cluster

  replicas = @cluster.find_replicas(keyspace, statement)
  return @policy.plan(keyspace, statement, options) if replicas.empty?

  replicas = if @shuffle
               replicas.shuffle
             else
               replicas.dup
             end

  Plan.new(replicas, @policy, keyspace, statement, options)
end

#setup(cluster) ⇒ Object 



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 113

def setup(cluster)
  @cluster = cluster
  @policy.setup(cluster)
  nil
end

#teardown(cluster) ⇒ Object 



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# File 'lib/cassandra/load_balancing/policies/token_aware.rb', line 119

def teardown(cluster)
  @cluster = nil
  @policy.teardown(cluster)
  nil
end