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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.
*/
#include <cmath>
#include <cstdlib>
#include "mongo/db/mirroring_sampler.h"
namespace mongo {
MirroringSampler::SamplingParameters::SamplingParameters(const double ratio_,
const int rndMax,
const int rndValue)
: ratio{ratio_}, max{rndMax}, value{rndValue} {
invariant(ratio <= 1.0);
invariant(ratio >= 0.0);
invariant(value <= max);
invariant(value >= 0);
}
MirroringSampler::SamplingParameters::SamplingParameters(const double ratio,
const int rndMax,
RandomFunc rnd)
: SamplingParameters(ratio, rndMax, [&] {
if (ratio == 0.0) {
// We should never sample, avoid invoking rnd().
return rndMax;
}
if (ratio == 1.0) {
// We should always sample, avoid invoking rnd().
return 0;
}
return std::move(rnd)();
}()) {}
bool MirroringSampler::shouldSample(const SamplingParameters& params) const noexcept {
// If our value is less than our max, then take a sample.
return params.value < static_cast<int>(params.max * params.ratio);
}
std::vector<HostAndPort> MirroringSampler::getRawMirroringTargets(
const std::shared_ptr<const repl::IsMasterResponse>& isMaster) noexcept {
invariant(isMaster);
if (!isMaster->isMaster()) {
// Don't mirror if we're not primary
return {};
}
const auto& hosts = isMaster->getHosts();
if (hosts.size() < 2) {
// Don't mirror if we're standalone
return {};
}
const auto& self = isMaster->getPrimary();
std::vector<HostAndPort> potentialTargets;
for (auto& host : hosts) {
if (host != self) {
potentialTargets.push_back(host);
}
}
return potentialTargets;
}
std::vector<HostAndPort> MirroringSampler::getMirroringTargets(
const std::shared_ptr<const repl::IsMasterResponse>& isMaster,
const double ratio,
RandomFunc rnd,
const int rndMax) noexcept {
auto sampler = MirroringSampler();
auto samplingParams = SamplingParameters(ratio, rndMax, std::move(rnd));
if (!sampler.shouldSample(samplingParams)) {
return {};
}
return sampler.getRawMirroringTargets(isMaster);
}
} // namespace mongo
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