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/**
* Copyright (C) 2021-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 <boost/optional.hpp>
#include "mongo/bson/oid.h"
namespace mongo::sdam {
// Comparable pair or ElectionId (term) and SetVersion.
struct ElectionIdSetVersionPair {
const boost::optional<mongo::OID> electionId;
const boost::optional<int> setVersion;
bool allDefined() const {
return electionId && setVersion;
}
bool allUndefined() const {
return !electionId && !setVersion;
}
};
inline bool electionIdEqual(const ElectionIdSetVersionPair& p1,
const ElectionIdSetVersionPair& p2) {
return p1.electionId && p2.electionId && (*p1.electionId).compare(*p2.electionId) == 0;
}
inline bool operator<(const ElectionIdSetVersionPair& p1, const ElectionIdSetVersionPair& p2) {
if (electionIdEqual(p1, p2)) {
if (p1.setVersion && p2.setVersion) {
return *p1.setVersion < *p2.setVersion;
}
return false; // Cannot compare Set versions.
}
if (p1.electionId && p2.electionId) {
return (*p1.electionId).compare(*p2.electionId) < 0;
}
// We know that election Ids are not comparable.
return false;
}
inline bool operator>(const ElectionIdSetVersionPair& p1, const ElectionIdSetVersionPair& p2) {
return p2 < p1;
}
// Equality operator is not equivalent to "!< && !>" because of grey area of undefined values.
inline bool operator==(const ElectionIdSetVersionPair& p1, const ElectionIdSetVersionPair& p2) {
if (!electionIdEqual(p1, p2)) {
return false;
}
if (!p1.setVersion && !p2.setVersion) {
return true;
}
return p1.setVersion && p2.setVersion && *p1.setVersion == *p2.setVersion;
}
inline bool setVersionWentBackwards(const ElectionIdSetVersionPair& current,
const ElectionIdSetVersionPair& incoming) {
return current.setVersion && incoming.setVersion && *current.setVersion > *incoming.setVersion;
}
/**
* @return true if 'incoming' is RS primary and fields have consistent values.
*/
inline bool isIncomingPrimaryConsistent(const ElectionIdSetVersionPair& current,
const ElectionIdSetVersionPair& incoming) {
// If coming from primary both election Id and Set version should be always set.
// This requirement is true for at least MDB >= 4.0.
if (!incoming.electionId || !incoming.setVersion) {
return false;
}
if (current.allUndefined()) {
return true; // Further check is not necessary.
}
// Identical term means Set version should be equal or advance because no failover
// happened and Set version at the same primary cannot go backwards.
if (electionIdEqual(current, incoming)) {
return !current.setVersion || *current.setVersion <= *incoming.setVersion;
}
// If Set version goes backwards the term should advance, because it means
// failover happened. This is possible if the previous primary failed to replicate
// new Set version before failover. When it happens, we will rollback the Set version.
if (setVersionWentBackwards(current, incoming)) {
return !current.electionId || (*current.electionId).compare(*incoming.electionId) < 0;
}
return true;
}
} // namespace mongo::sdam
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