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#pragma once
#include <chrono>
#include <cstdint>
#include <mutex>
#include <vector>
#include "prometheus/client_metric.h"
#include "prometheus/detail/builder.h" // IWYU pragma: export
#include "prometheus/detail/ckms_quantiles.h"
#include "prometheus/detail/core_export.h"
#include "prometheus/detail/time_window_quantiles.h"
#include "prometheus/metric_type.h"
namespace prometheus {
/// \brief A summary metric samples observations over a sliding window of time.
///
/// This class represents the metric type summary:
/// https://prometheus.io/docs/instrumenting/writing_clientlibs/#summary
///
/// A summary provides a total count of observations and a sum of all observed
/// values. In contrast to a histogram metric it also calculates configurable
/// Phi-quantiles over a sliding window of time.
///
/// The essential difference between summaries and histograms is that summaries
/// calculate streaming Phi-quantiles on the client side and expose them
/// directly, while histograms expose bucketed observation counts and the
/// calculation of quantiles from the buckets of a histogram happens on the
/// server side:
/// https://prometheus.io/docs/prometheus/latest/querying/functions/#histogram_quantile.
///
/// Note that Phi designates the probability density function of the standard
/// Gaussian distribution.
///
/// See https://prometheus.io/docs/practices/histograms/ for detailed
/// explanations of Phi-quantiles, summary usage, and differences to histograms.
///
/// The class is thread-safe. No concurrent call to any API of this type causes
/// a data race.
class PROMETHEUS_CPP_CORE_EXPORT Summary {
public:
using Quantiles = std::vector<detail::CKMSQuantiles::Quantile>;
static const MetricType metric_type{MetricType::Summary};
/// \brief Create a summary metric.
///
/// \param quantiles A list of 'targeted' Phi-quantiles. A targeted
/// Phi-quantile is specified in the form of a Phi-quantile and tolerated
/// error. For example a Quantile{0.5, 0.1} means that the median (= 50th
/// percentile) should be returned with 10 percent error or a Quantile{0.2,
/// 0.05} means the 20th percentile with 5 percent tolerated error. Note that
/// percentiles and quantiles are the same concept, except percentiles are
/// expressed as percentages. The Phi-quantile must be in the interval [0, 1].
/// Note that a lower tolerated error for a Phi-quantile results in higher
/// usage of resources (memory and cpu) to calculate the summary.
///
/// The Phi-quantiles are calculated over a sliding window of time. The
/// sliding window of time is configured by max_age and age_buckets.
///
/// \param max_age Set the duration of the time window, i.e., how long
/// observations are kept before they are discarded. The default value is 60
/// seconds.
///
/// \param age_buckets Set the number of buckets of the time window. It
/// determines the number of buckets used to exclude observations that are
/// older than max_age from the summary, e.g., if max_age is 60 seconds and
/// age_buckets is 5, buckets will be switched every 12 seconds. The value is
/// a trade-off between resources (memory and cpu for maintaining the bucket)
/// and how smooth the time window is moved. With only one age bucket it
/// effectively results in a complete reset of the summary each time max_age
/// has passed. The default value is 5.
Summary(const Quantiles& quantiles,
std::chrono::milliseconds max_age = std::chrono::seconds{60},
int age_buckets = 5);
/// \brief Observe the given amount.
void Observe(double value);
/// \brief Get the current value of the summary.
///
/// Collect is called by the Registry when collecting metrics.
ClientMetric Collect() const;
private:
const Quantiles quantiles_;
mutable std::mutex mutex_;
std::uint64_t count_;
double sum_;
detail::TimeWindowQuantiles quantile_values_;
};
/// \brief Return a builder to configure and register a Summary metric.
///
/// @copydetails Family<>::Family()
///
/// Example usage:
///
/// \code
/// auto registry = std::make_shared<Registry>();
/// auto& summary_family = prometheus::BuildSummary()
/// .Name("some_name")
/// .Help("Additional description.")
/// .Labels({{"key", "value"}})
/// .Register(*registry);
///
/// ...
/// \endcode
///
/// \return An object of unspecified type T, i.e., an implementation detail
/// except that it has the following members:
///
/// - Name(const std::string&) to set the metric name,
/// - Help(const std::string&) to set an additional description.
/// - Labels(const Labels&) to assign a set of
/// key-value pairs (= labels) to the metric.
///
/// To finish the configuration of the Summary metric register it with
/// Register(Registry&).
PROMETHEUS_CPP_CORE_EXPORT detail::Builder<Summary> BuildSummary();
} // namespace prometheus
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