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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.
*/
#include <algorithm> // std::sort
#include <cmath> // std::pow
#include <functional> // std::greater
#include "mongo/db/query/optimizer/utils/ce_math.h"
#include "mongo/util/assert_util.h"
namespace mongo::optimizer::ce {
bool validSelectivity(SelectivityType sel) {
return (sel >= 0.0 && sel <= 1.0);
}
bool validCardinality(CEType card) {
return (card >= kMinCard && card <= std::numeric_limits<double>::max());
}
/**
* Conditionally negate selectivity.
*/
template <bool negate>
constexpr SelectivityType maybeNegate(const SelectivityType s) {
return negateSel(s);
}
template <>
constexpr SelectivityType maybeNegate<false>(const SelectivityType s) {
return s;
}
/**
* Computes conjunctive and disjunctive exponential backoff. We first take the extreme selectivities
* (the smallest for conjunction, or the largest for disjunction). We then multiply them together
* (inverting them for disjunction), and then for disjunction we invert the result, applying
* increasing decay factor for each larger/smaller selectivity.
*/
template <bool isConjunction,
class Comparator = typename std::conditional_t<isConjunction,
std::less<SelectivityType>,
std::greater<SelectivityType>>>
SelectivityType expBackoffInternal(std::vector<SelectivityType> sels) {
if (sels.size() == 1) {
return sels[0];
}
const size_t actualMaxBackoffElements = std::min(sels.size(), kMaxBackoffElements);
std::partial_sort(
sels.begin(), sels.begin() + actualMaxBackoffElements, sels.end(), Comparator());
SelectivityType sel{1.0};
double f = 1.0;
for (size_t i = 0; i < actualMaxBackoffElements; i++, f /= 2.0) {
sel *= maybeNegate<!isConjunction>(sels[i]).pow(f);
}
return maybeNegate<!isConjunction>(sel);
}
SelectivityType conjExponentialBackoff(std::vector<SelectivityType> conjSelectivities) {
uassert(6749501,
"The array of conjunction selectivities may not be empty.",
!conjSelectivities.empty());
return expBackoffInternal<true /*isConjunction*/>(std::move(conjSelectivities));
}
SelectivityType disjExponentialBackoff(std::vector<SelectivityType> disjSelectivities) {
uassert(6749502,
"The array of disjunction selectivities may not be empty.",
!disjSelectivities.empty());
return expBackoffInternal<false /*isConjunction*/>(std::move(disjSelectivities));
}
} // namespace mongo::optimizer::ce
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