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/**
* Copyright (C) 2018-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 "mongo/bson/bsonelement.h"
#include "mongo/bson/util/builder.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/storage/storage_options.h"
#include "mongo/stdx/mutex.h"
namespace mongo {
/**
* A KVPrefix may be prepended to the keys of entries in an underlying KV store. Prefixing keys as
* such allows multiple MongoDB collections share an underlying table. This can be a beneficial
* tradeoff for workloads that create many collections.
*/
class KVPrefix {
public:
// Represents a table that is not grouped and should not have its keys prefixed.
static const KVPrefix kNotPrefixed;
bool isPrefixed() const {
return _value >= 0;
}
int64_t toBSONValue() const {
return _value;
}
int64_t repr() const {
return _value;
}
std::string toString() const;
inline bool operator<(const KVPrefix& rhs) const {
return _value < rhs._value;
}
inline bool operator==(const KVPrefix& rhs) const {
return _value == rhs._value;
}
inline bool operator!=(const KVPrefix& rhs) const {
return _value != rhs._value;
}
static KVPrefix fromBSONElement(const BSONElement value);
static void setLargestPrefix(KVPrefix largestPrefix);
/**
* Returns 'KVPrefix::kNotPrefixed' if 'storageGlobalParams.groupCollections' is false or the
* input 'ns' is a namespace disallowed for grouping. Otherwise returns the next 'KVPrefix'
* ensuring it is unique with respect to active collections and indexes.
*/
static KVPrefix getNextPrefix(const NamespaceString& ns);
/**
* Unconditionally returns a new prefix. Only useful for testing.
*/
static KVPrefix generateNextPrefix();
private:
explicit KVPrefix(int64_t value) : _value(value) {}
int64_t _value;
static stdx::mutex _nextValueMutex;
static int64_t _nextValue;
};
inline std::ostream& operator<<(std::ostream& s, const KVPrefix& prefix) {
return (s << prefix.toString());
}
}
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