/// <summary>
/// Construct an Epsilon Greedy HostPool
///
/// Epsilon Greedy is an algorithm that allows HostPool not only to track failure state,
/// but also to learn about "better" options in terms of speed, and to pick from available hosts
/// based on how well they perform. This gives a weighted request rate to better
/// performing hosts, while still distributing requests to all hosts (proportionate to their performance).
///
/// A good overview of Epsilon Greedy is here http://stevehanov.ca/blog/index.php?id=132
///
/// To compute the weighting scores, we perform a weighted average of recent response times, over the course of
/// `decayDuration`. decayDuration may be set to null to use the default value of 5 minutes
/// We then use the supplied EpsilonValueCalculator to calculate a score from that weighted average response time.
/// </summary>
/// <param name="retryDelayInitial">The initial retry delay when a host goes down. Default, null, is 30 seconds.</param>
/// <param name="retryDelayMax">The maximum retry delay when a host goes down. Default, null, is 15 minutes.</param>
/// <param name="decayDuration">The amount of time to cycle through all EpsilonBuckets (0...120).
/// This decay duration is divided by EpsilonBuckets (default: 5 min / 120 buckets = 2.5 seconds per bucket).
/// IE: The average will be taken every decayDuration/EpsilonBuckets seconds.</param>
/// <param name="calc">Given the weighted average among EpsilonBuckets slot measurements, calculate the host's EpsilonValue using EpsilonCalculators.Linear/Logarithmic/Polynomial(exponent)</param>
/// <param name="autoStartDecayTimer">Automatically starts the decay timer. If false, you need to call StartDecayTimer manually for epsilon values to be calculated correctly.</param>
public EpsilonGreedyHostPool(
TimeSpan?retryDelayInitial,
TimeSpan?retryDelayMax,
TimeSpan?decayDuration,
EpsilonValueCalculator calc,
bool autoStartDecayTimer = true)
: base(retryDelayInitial, retryDelayMax)
{
this.decayDuration = decayDuration ?? DefaultDecayDuration;
this.calc = calc;
this.epsilon = InitialEpsilon;
this.weights = Enumerable.Range(1, EpsilonBuckets)
.Select(i => i / Convert.ToSingle(EpsilonBuckets))
.ToArray();
if (autoStartDecayTimer)
{
StartDecayTimer();
}
}
/// <summary>
/// Construct an Epsilon Greedy HostPool
///
/// Epsilon Greedy is an algorithm that allows HostPool not only to track failure state,
/// but also to learn about "better" options in terms of speed, and to pick from available hosts
/// based on how well they perform. This gives a weighted request rate to better
/// performing hosts, while still distributing requests to all hosts (proportionate to their performance).
///
/// A good overview of Epsilon Greedy is here http://stevehanov.ca/blog/index.php?id=132
///
/// To compute the weighting scores, we perform a weighted average of recent response times, over the course of
/// `decayDuration`. decayDuration may be set to null to use the default value of 5 minutes
/// We then use the supplied EpsilonValueCalculator to calculate a score from that weighted average response time.
/// </summary>
/// <param name="decayDuration">The amount of time to cycle though all EpsilonBuckets (0...120).
/// This decay duration is divided by EpsilonBuckets (default: 5 min / 120 buckets = 2.5 seconds per bucket).
/// IE: The average will be taken every decayDuration/EpsilonBuckets seconds.</param>
/// <param name="calc">Given the weighted average among EpsilonBuckets slot measurements, calculate the host's EpsilonValue using EpsilonCalculators.Linear/Logarithmic/Polynomial(exponent)</param>
/// <param name="autoStartDecayTimer">Automatically starts the decay timer. If false, you need to call StartDecayTimer manually for epsilon values to be calculated correctly.</param>
public EpsilonGreedyHostPool(TimeSpan?decayDuration,
EpsilonValueCalculator calc,
bool autoStartDecayTimer = true) :
this(null, null, decayDuration, calc, autoStartDecayTimer)
{
}
