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101 lines
3.4 KiB
101 lines
3.4 KiB
from __future__ import absolute_import
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import abc
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from kafka.metrics.measurable_stat import AbstractMeasurableStat
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class AbstractSampledStat(AbstractMeasurableStat):
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"""
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An AbstractSampledStat records a single scalar value measured over
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one or more samples. Each sample is recorded over a configurable
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window. The window can be defined by number of events or elapsed
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time (or both, if both are given the window is complete when
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*either* the event count or elapsed time criterion is met).
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All the samples are combined to produce the measurement. When a
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window is complete the oldest sample is cleared and recycled to
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begin recording the next sample.
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Subclasses of this class define different statistics measured
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using this basic pattern.
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"""
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__metaclass__ = abc.ABCMeta
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def __init__(self, initial_value):
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self._initial_value = initial_value
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self._samples = []
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self._current = 0
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@abc.abstractmethod
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def update(self, sample, config, value, time_ms):
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raise NotImplementedError
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@abc.abstractmethod
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def combine(self, samples, config, now):
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raise NotImplementedError
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def record(self, config, value, time_ms):
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sample = self.current(time_ms)
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if sample.is_complete(time_ms, config):
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sample = self._advance(config, time_ms)
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self.update(sample, config, float(value), time_ms)
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sample.event_count += 1
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def new_sample(self, time_ms):
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return self.Sample(self._initial_value, time_ms)
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def measure(self, config, now):
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self.purge_obsolete_samples(config, now)
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return float(self.combine(self._samples, config, now))
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def current(self, time_ms):
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if not self._samples:
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self._samples.append(self.new_sample(time_ms))
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return self._samples[self._current]
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def oldest(self, now):
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if not self._samples:
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self._samples.append(self.new_sample(now))
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oldest = self._samples[0]
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for sample in self._samples[1:]:
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if sample.last_window_ms < oldest.last_window_ms:
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oldest = sample
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return oldest
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def purge_obsolete_samples(self, config, now):
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"""
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Timeout any windows that have expired in the absence of any events
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"""
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expire_age = config.samples * config.time_window_ms
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for sample in self._samples:
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if now - sample.last_window_ms >= expire_age:
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sample.reset(now)
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def _advance(self, config, time_ms):
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self._current = (self._current + 1) % config.samples
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if self._current >= len(self._samples):
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sample = self.new_sample(time_ms)
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self._samples.append(sample)
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return sample
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else:
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sample = self.current(time_ms)
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sample.reset(time_ms)
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return sample
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class Sample(object):
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def __init__(self, initial_value, now):
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self.initial_value = initial_value
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self.event_count = 0
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self.last_window_ms = now
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self.value = initial_value
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def reset(self, now):
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self.event_count = 0
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self.last_window_ms = now
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self.value = self.initial_value
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def is_complete(self, time_ms, config):
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return (time_ms - self.last_window_ms >= config.time_window_ms or
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self.event_count >= config.event_window)
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