Summary: In get operations, merge_operands is only used in few cases. Lazily initialize it can reduce average latency in some cases Test Plan: make all check Reviewers: haobo, kailiu, dhruba Reviewed By: haobo CC: igor, nkg-, leveldb Differential Revision: https://reviews.facebook.net/D14415main
Siying Dong
11 years ago
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90729f8b23
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// Copyright (c) 2013, 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 "db/dbformat.h" |
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#include "rocksdb/slice.h" |
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#include <string> |
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#include <deque> |
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namespace rocksdb { |
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const std::deque<std::string> 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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} |
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} |
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// Replace the first two operands of merge_result, which are expected be the
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// merge results of them.
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void PushPartialMergeResult(std::string& merge_result) { |
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assert (operand_list); |
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operand_list->pop_front(); |
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swap(operand_list->front(), merge_result); |
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} |
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// Push a merge operand
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void PushOperand(const Slice& operand_slice) { |
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Initialize(); |
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operand_list->push_front(operand_slice.ToString()); |
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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) const { |
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assert (operand_list); |
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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::deque<std::string>& GetOperands() const { |
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if (!operand_list) { |
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return empty_operand_list; |
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} |
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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::deque<std::string>()); |
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} |
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} |
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std::unique_ptr<std::deque<std::string>> operand_list; |
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}; |
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} // namespace rocksdb
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