mirror of
https://github.com/facebook/rocksdb.git
synced 2024-11-25 22:44:05 +00:00
ef2211a9ca
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/D14415
70 lines
1.9 KiB
C++
70 lines
1.9 KiB
C++
// Copyright (c) 2013, 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 the first two operands of merge_result, which are expected be the
|
|
// merge results of them.
|
|
void PushPartialMergeResult(std::string& merge_result) {
|
|
assert (operand_list);
|
|
operand_list->pop_front();
|
|
swap(operand_list->front(), 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
|
|
|