histogram_metrics_helper.hh

/*
 * Copyright (C) 2020-present ScyllaDB
 *
 * Modified by ScyllaDB
 */

/*
 * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
 */

#pragma once

#include <cstdint>
#include <seastar/core/metrics_types.hh>
#include "seastarx.hh"
#include "estimated_histogram.hh"
#include "histogram.hh"

template<uint64_t Min, uint64_t Max, size_t Precision>
seastar::metrics::histogram to_metrics_histogram(const utils::approx_exponential_histogram<Min, Max, Precision>& hist) {
    seastar::metrics::histogram res;
    static constexpr size_t MIN_ID = log2ceil(Min) * Precision + 1;
    static constexpr size_t Schema = log2floor(Precision);
    res.buckets.resize(hist.size() - 1);
    uint64_t cummulative_count = 0;
    res.sample_sum = 0;
    res.native_histogram = seastar::metrics::native_histogram_info{Schema, MIN_ID};
    for (size_t i = 0; i < hist.NUM_BUCKETS - 1; i++) {
        auto& v = res.buckets[i];
        v.upper_bound = hist.get_bucket_lower_limit(i + 1);
        cummulative_count += hist.get(i);
        v.count = cummulative_count;
        res.sample_sum += hist.get(i) * v.upper_bound;
    }
    // The count serves as the infinite bucket
    res.sample_count = cummulative_count + hist.get(hist.NUM_BUCKETS - 1);
    res.sample_sum += hist.get(hist.NUM_BUCKETS - 1) * hist.get_bucket_lower_limit(hist.NUM_BUCKETS - 1);
    return res;
}

/*!
 * \brief get a metrics summary from timed_rate_moving_average_with_summary
 *
 * timed_rate_moving_average_with_summary contains a summary. This function
 * copy it to a metric summary.
 * A metric summary is a histogram where each bucket holds some quantile.
 */
seastar::metrics::histogram to_metrics_summary(const utils::summary_calculator& summary) noexcept;