55 lines
1.7 KiB
Python
55 lines
1.7 KiB
Python
from collections import namedtuple
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CubicParams = namedtuple('CubicParams', ['w_max', 'k', 'last_fail'])
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class CubicCalculator(object):
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_SCALE_CONSTANT = 0.4
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_BETA = 0.7
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def __init__(self, starting_max_rate,
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start_time,
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scale_constant=_SCALE_CONSTANT, beta=_BETA):
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self._w_max = starting_max_rate
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self._scale_constant = scale_constant
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self._beta = beta
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self._k = self._calculate_zero_point()
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self._last_fail = start_time
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def _calculate_zero_point(self):
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k = ((self._w_max * (1 - self._beta)) / self._scale_constant) ** (1 / 3.0)
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return k
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def success_received(self, timestamp):
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dt = timestamp - self._last_fail
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new_rate = (
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self._scale_constant * (dt - self._k) ** 3 + self._w_max
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)
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return new_rate
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def error_received(self, current_rate, timestamp):
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# Consider not having this be the current measured rate.
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# We have a new max rate, which is the current rate we were sending
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# at when we received an error response.
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self._w_max = current_rate
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self._k = self._calculate_zero_point()
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self._last_fail = timestamp
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return current_rate * self._beta
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def get_params_snapshot(self):
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"""Return a read-only object of the current cubic parameters.
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These parameters are intended to be used for debug/troubleshooting
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purposes. These object is a read-only snapshot and cannot be used
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to modify the behavior of the CUBIC calculations.
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New parameters may be added to this object in the future.
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"""
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return CubicParams(
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w_max=self._w_max,
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k=self._k,
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last_fail=self._last_fail
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)
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