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/**
* Copyright (C) 2022-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <cstdint>
#include <string>
#include <utility>
#include <vector>
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/db/commands/server_status_metric.h"
#include "mongo/util/histogram.h"
namespace mongo {
/**
* Records samples, exposing the aggregate statistics in Server Status as a
* Histogram.
*
* The histogram is represented as a BSON array of bucket BSON
* objects.
*
* Like all ServerStatusMetric counters, instances of this class should
* be static duration objects at namespace scope.
*/
class HistogramServerStatusMetric {
public:
HistogramServerStatusMetric(std::string name, std::vector<uint64_t> bounds)
: _hist{std::move(bounds)},
_metric(addMetricToTree(std::make_unique<Metric>(std::move(name), this))) {}
void increment(uint64_t value) {
_hist.increment(value);
}
/**
* Returns an exponential sequence of `sz` elements. Starts at `base`
* and increase by a ratio of `rate` between successive elements.
* This is used to make a `bounds` argument for the constructor.
*/
static std::vector<uint64_t> pow(size_t sz, uint64_t base, uint64_t rate) {
std::vector<uint64_t> v;
v.reserve(sz);
for (; sz--; base *= rate)
v.push_back(base);
return v;
}
private:
class Metric : public ServerStatusMetric {
public:
Metric(std::string name, const HistogramServerStatusMetric* owner)
: ServerStatusMetric{std::move(name)}, _owner{owner} {}
void appendAtLeaf(BSONObjBuilder& bob) const override {
_owner->_appendTo(_leafName, bob);
}
private:
const HistogramServerStatusMetric* const _owner;
};
void _appendTo(StringData leafName, BSONObjBuilder& bob) const {
BSONArrayBuilder arr{bob.subarrayStart(leafName)};
for (auto&& [count, lower, upper] : _hist)
BSONObjBuilder(arr.subobjStart())
.append("lowerBound", static_cast<long long>(lower ? *lower : 0))
.append("count", count);
}
Histogram<uint64_t> _hist;
Metric& _metric;
};
} // namespace mongo
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