Class: Gitlab::Database::LoadBalancing::ServiceDiscovery::Sampler

Inherits:
Object
  • Object
show all
Defined in:
lib/gitlab/database/load_balancing/service_discovery/sampler.rb

Instance Method Summary collapse

Constructor Details

#initialize(max_replica_pools:, seed: Random.new_seed) ⇒ Sampler

Returns a new instance of Sampler.



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# File 'lib/gitlab/database/load_balancing/service_discovery/sampler.rb', line 8

def initialize(max_replica_pools:, seed: Random.new_seed)
  # seed must be set once and consistent
  # for every invocation of #sample on
  # the same instance of Sampler
  @seed = seed
  @max_replica_pools = max_replica_pools
end

Instance Method Details

#sample(addresses) ⇒ Object 



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# File 'lib/gitlab/database/load_balancing/service_discovery/sampler.rb', line 16

def sample(addresses)
  return addresses if @max_replica_pools.nil? || addresses.count <= @max_replica_pools

  ::Gitlab::Database::LoadBalancing::Logger.debug(
    event: :host_list_limit_exceeded,
    message: "Host list length exceeds max_replica_pools so random hosts will be chosen.",
    max_replica_pools: @max_replica_pools,
    total_host_list_length: addresses.count,
    randomization_seed: @seed
  )

  # First sort them in case the ordering from DNS server changes
  # then randomly order all addresses using consistent seed so
  # this process always gives the same set for this instance of
  # Sampler
  addresses = addresses.sort
  addresses = addresses.shuffle(random: Random.new(@seed))

  # Group by hostname so that we can sample evenly across hosts
  addresses_by_host = addresses.group_by(&:hostname)

  selected_addresses = []
  while selected_addresses.count < @max_replica_pools
    # Loop over all hostnames grabbing one address at a time to
    # evenly distribute across all hostnames
    addresses_by_host.each do |host, addresses|
      next if addresses.empty?

      selected_addresses << addresses.pop

      break unless selected_addresses.count < @max_replica_pools
    end
  end

  selected_addresses
end