mirror of https://github.com/facebook/rocksdb.git
117 lines
3.2 KiB
C++
117 lines
3.2 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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#pragma once
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#include <string>
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#include <vector>
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#include "db/dbformat.h"
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#include "rocksdb/slice.h"
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namespace rocksdb {
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const std::vector<Slice> empty_operand_list;
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// The merge context for merging a user key.
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// When doing a Get(), DB will create such a class and pass it when
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// issuing Get() operation to memtables and version_set. The operands
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// will be fetched from the context when issuing partial of full merge.
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class MergeContext {
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public:
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// Clear all the operands
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void Clear() {
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if (operand_list_) {
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operand_list_->clear();
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copied_operands_->clear();
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}
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}
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// Push a merge operand
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void PushOperand(const Slice& operand_slice, bool operand_pinned = false) {
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Initialize();
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SetDirectionBackward();
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if (operand_pinned) {
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operand_list_->push_back(operand_slice);
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} else {
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// We need to have our own copy of the operand since it's not pinned
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copied_operands_->emplace_back(
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new std::string(operand_slice.data(), operand_slice.size()));
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operand_list_->push_back(*copied_operands_->back());
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}
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}
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// Push back a merge operand
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void PushOperandBack(const Slice& operand_slice,
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bool operand_pinned = false) {
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Initialize();
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SetDirectionForward();
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if (operand_pinned) {
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operand_list_->push_back(operand_slice);
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} else {
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// We need to have our own copy of the operand since it's not pinned
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copied_operands_->emplace_back(
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new std::string(operand_slice.data(), operand_slice.size()));
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operand_list_->push_back(*copied_operands_->back());
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}
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}
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// return total number of operands in the list
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size_t GetNumOperands() const {
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if (!operand_list_) {
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return 0;
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}
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return operand_list_->size();
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}
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// Get the operand at the index.
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Slice GetOperand(int index) {
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assert(operand_list_);
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SetDirectionForward();
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return (*operand_list_)[index];
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}
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// Return all the operands.
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const std::vector<Slice>& GetOperands() {
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if (!operand_list_) {
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return empty_operand_list;
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}
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SetDirectionForward();
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return *operand_list_;
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}
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private:
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void Initialize() {
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if (!operand_list_) {
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operand_list_.reset(new std::vector<Slice>());
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copied_operands_.reset(new std::vector<std::unique_ptr<std::string>>());
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}
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}
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void SetDirectionForward() {
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if (operands_reversed_ == true) {
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std::reverse(operand_list_->begin(), operand_list_->end());
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operands_reversed_ = false;
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}
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}
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void SetDirectionBackward() {
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if (operands_reversed_ == false) {
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std::reverse(operand_list_->begin(), operand_list_->end());
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operands_reversed_ = true;
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}
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}
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// List of operands
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std::unique_ptr<std::vector<Slice>> operand_list_;
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// Copy of operands that are not pinned.
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std::unique_ptr<std::vector<std::unique_ptr<std::string>>> copied_operands_;
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bool operands_reversed_ = true;
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};
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} // namespace rocksdb
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