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/**
* Copyright (C) 2020-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 <functional>
#include <memory>
#include <vector>
#include "mongo/db/repl/hello_response.h"
#include "mongo/platform/random.h"
#include "mongo/util/net/hostandport.h"
#include "mongo/util/static_immortal.h"
#include "mongo/util/synchronized_value.h"
namespace mongo {
/**
* Populates a random subset of eligible secondaries (using `HelloResponse`
* and a ratio) for mirroring. An empty subset for eligible secondaries indicates
* no mirroring is necessary/possible.
*/
class MirroringSampler final {
public:
using RandomFunc = std::function<int()>;
static int threadSafeRandom() {
static StaticImmortal<synchronized_value<PseudoRandom>> random{
PseudoRandom{SecureRandom{}.nextInt64()}};
return (*random)->nextInt32(defaultRandomMax());
}
static RandomFunc defaultRandomFunc() {
return threadSafeRandom;
}
static constexpr int defaultRandomMax() {
return RAND_MAX;
};
/**
* Sampling parameters for mirroring commands to eligible secondaries.
*
* Note that the value member is a raw integer and thus can be normalized to fit different
* interpretations of ratio.
*/
struct SamplingParameters {
explicit SamplingParameters(double ratio, int rndMax, int rndValue);
/**
* Construct with a value from rnd().
*/
explicit SamplingParameters(double ratio, int rndMax, RandomFunc rnd);
/**
* Construct with a value from defaultRandomFunc().
*/
explicit SamplingParameters(const double ratio)
: SamplingParameters(ratio, defaultRandomMax(), defaultRandomFunc()) {}
const double ratio;
const int max;
const int value;
};
/**
* Use the given imr and params to determine if we should attempt to sample.
*/
bool shouldSample(const std::shared_ptr<const repl::HelloResponse>& imr,
const SamplingParameters& params) const noexcept;
/**
* Return all eligible hosts from a HelloResponse that we should mirror to.
*/
std::vector<HostAndPort> getRawMirroringTargets(
const std::shared_ptr<const repl::HelloResponse>& isMaster) noexcept;
/**
* Approximate use of the MirroringSampler for testing.
*
* In practice, we call constituent functions in sequence to pessimistically spare work.
*/
static std::vector<HostAndPort> getMirroringTargets(
const std::shared_ptr<const repl::HelloResponse>& isMaster,
double ratio,
RandomFunc rnd = defaultRandomFunc(),
int rndMax = defaultRandomMax()) noexcept;
};
} // namespace mongo
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