Instruments

Gauges

class metrology.instruments.gauge.Gauge

A gauge is an instantaneous measurement of a value

class JobGauge(metrology.instruments.Gauge):
    @property
    def value(self):
        return len(queue)

gauge = Metrology.gauge('pending-jobs', JobGauge())
class metrology.instruments.gauge.PercentGauge

A percent gauge is a ratio gauge where the result is normalized to a value between 0 and 100.

class metrology.instruments.gauge.RatioGauge

A ratio gauge is a simple way to create a gauge which is the ratio between two numbers.

Counters

class metrology.instruments.counter.Counter

A counter is like a gauge, but you can increment or decrement its value

counter = Metrology.counter('pending-jobs')
counter.increment()
counter.decrement()
counter.count
count

Return the current value of the counter.

decrement(value=1)

Decrement the counter. By default it will decrement by 1.

Parameters:value – value to decrement the counter.
increment(value=1)

Increment the counter. By default it will increment by 1.

Parameters:value – value to increment the counter.

Derive

class metrology.instruments.derive.Derive(average_class=<class 'metrology.stats.ewma.EWMA'>)

A derive is like a meter but accepts an absolute counter as input.

derive = Metrology.derive(‘network.io’) derive.mark() derive.count
mark(value=1)

Record an event with the derive.

Parameters:value – counter value to record

Meters

class metrology.instruments.meter.Meter(average_class=<class 'metrology.stats.ewma.EWMA'>)

A meter measures the rate of events over time (e.g., “requests per second”).

In addition to the mean rate, you can also track 1, 5 and 15 minutes moving averages

meter = Metrology.meter('requests')
meter.mark()
meter.count
count

Returns the total number of events that have been recorded.

fifteen_minute_rate

Returns the fifteen-minute average rate.

five_minute_rate

Returns the five-minute average rate.

mark(*args, **kwargs)

Record an event with the meter. By default it will record one event.

Parameters:value – number of event to record
mean_rate

Returns the mean rate of the events since the start of the process.

one_minute_rate

Returns the one-minute average rate.

Histograms

class metrology.instruments.histogram.Histogram(sample)

A histogram measures the statistical distribution of values in a stream of data. In addition to minimum, maximum, mean, it also measures median, 75th, 90th, 95th, 98th, 99th, and 99.9th percentiles

histogram = Metrology.histogram('response-sizes')
histogram.update(len(response.content))

Metrology provides two types of histograms: uniform and exponentially decaying.

count

Return number of values.

max

Returns the maximun value.

mean

Returns the mean value.

min

Returns the minimum value.

stddev

Returns the standard deviation.

total

Returns the total value.

variance

Returns variance

class metrology.instruments.histogram.HistogramExponentiallyDecaying

A exponentially decaying histogram produces quantiles which are representative of approximately the last five minutes of data.

Unlike the uniform histogram, a biased histogram represents recent data, allowing you to know very quickly if the distribution of the data has changed.

class metrology.instruments.histogram.HistogramUniform

A uniform histogram produces quantiles which are valid for the entirely of the histogram’s lifetime. It will return a median value, for example, which is the median of all the values the histogram has ever been updated with.

Use a uniform histogram when you’re interested in long-term measurements. Don’t use one where you’d want to know if the distribution of the underlying data stream has changed recently.

Timers and utilization timers

class metrology.instruments.timer.Timer(histogram=<class 'metrology.instruments.histogram.HistogramExponentiallyDecaying'>)

A timer measures both the rate that a particular piece of code is called and the distribution of its duration

timer = Metrology.timer('responses')
with timer:
    do_something()
count

Returns the number of measurements that have been made.

fifteen_minute_rate

Returns the fifteen-minute average rate.

five_minute_rate

Returns the five-minute average rate.

max

Returns the maximum amount of time spent in the operation.

mean

Returns the mean time spent in the operation.

mean_rate

Returns the mean rate of the events since the start of the process.

min

Returns the minimum amount of time spent in the operation.

one_minute_rate

Returns the one-minute average rate.

stddev

Returns the standard deviation of the mean spent in the operation.

total_time

Returns the total time spent.

update(duration)

Records the duration of an operation.

class metrology.instruments.timer.UtilizationTimer(histogram=<class 'metrology.instruments.histogram.HistogramExponentiallyDecaying'>)

A specialized timer that calculates the percentage of wall-clock time that was spent

utimer = Metrology.utilization_timer('responses')
with utimer:
  do_something()
count

Returns the number of measurements that have been made.

fifteen_minute_rate

Returns the fifteen-minute average rate.

fifteen_minute_utilization

Returns the fifteen-minute average utilization as a percentage.

five_minute_rate

Returns the five-minute average rate.

five_minute_utilization

Returns the five-minute average utilization as a percentage.

max

Returns the maximum amount of time spent in the operation.

mean

Returns the mean time spent in the operation.

mean_rate

Returns the mean rate of the events since the start of the process.

mean_utilization

Returns the mean (average) utilization as a percentage since the process started.

min

Returns the minimum amount of time spent in the operation.

one_minute_rate

Returns the one-minute average rate.

one_minute_utilization

Returns the one-minute average utilization as a percentage.

stddev

Returns the standard deviation of the mean spent in the operation.

total_time

Returns the total time spent.

Health Checks

class metrology.instruments.healthcheck.HealthCheck

A health check is a small self-test to verify that a specific component or responsibility is performing correctly

class DatabaseHealthCheck(metrology.healthcheck.HealthCheck):
    def __init__(self, database):
        self.database = database

    def check(self):
        if database.ping():
            return True
        return False

health_check = Metrology.health_check('database',
                                      DatabaseHealthCheck(database))
health_check.check()
check()

Returns True if what is being checked is healthy