rocksdb/db/merge_context.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#pragma once
#include "db/dbformat.h"
#include "rocksdb/slice.h"
#include <string>
#include <deque>
namespace rocksdb {
const std::deque<std::string> empty_operand_list;
// The merge context for merging a user key.
// When doing a Get(), DB will create such a class and pass it when
// issuing Get() operation to memtables and version_set. The operands
// will be fetched from the context when issuing partial of full merge.
class MergeContext {
public:
// Clear all the operands
void Clear() {
if (operand_list) {
operand_list->clear();
}
}
// Replace all operands with merge_result, which are expected to be the
// merge result of them.
void PushPartialMergeResult(std::string& merge_result) {
assert (operand_list);
operand_list->clear();
operand_list->push_front(std::move(merge_result));
}
// Push a merge operand
void PushOperand(const Slice& operand_slice) {
Initialize();
operand_list->push_front(operand_slice.ToString());
}
// return total number of operands in the list
size_t GetNumOperands() const {
if (!operand_list) {
return 0;
}
return operand_list->size();
}
// Get the operand at the index.
Slice GetOperand(int index) const {
assert (operand_list);
return (*operand_list)[index];
}
// Return all the operands.
const std::deque<std::string>& GetOperands() const {
if (!operand_list) {
return empty_operand_list;
}
return *operand_list;
}
private:
void Initialize() {
if (!operand_list) {
operand_list.reset(new std::deque<std::string>());
}
}
std::unique_ptr<std::deque<std::string>> operand_list;
};
} // namespace rocksdb