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修复(BUFFER): 修复lru_k_replacer.cpp当中Evict函数实现存在的边界问题 #2

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Merged
LunarStore merged 1 commit into from
Mar 3, 2025
Merged

修复(BUFFER): 修复lru_k_replacer.cpp当中Evict函数实现存在的边界问题 #2

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34 changes: 17 additions & 17 deletions src/buffer/buffer_pool_manager.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,7 @@ auto BufferPoolManager::NewPage(page_id_t *page_id) -> Page * {
*page_id = INVALID_PAGE_ID;
std::lock_guard<std::mutex> lock(latch_);

if(NewFrameUnlocked(frame_id) == nullptr) return nullptr;
if (NewFrameUnlocked(frame_id) == nullptr) return nullptr;

replacer_->RecordAccess(frame_id); // 确保frame存在于replacer中，并添加一条history
replacer_->SetEvictable(frame_id, false);
Expand All @@ -62,19 +62,19 @@ auto BufferPoolManager::NewPage(page_id_t *page_id) -> Page * {

auto BufferPoolManager::NewFrameUnlocked(frame_id_t &frame_id) -> Page *{
frame_id = -1; // 初始化为无效
if(!free_list_.empty()){
if (!free_list_.empty()) {
// 优先找free_list
frame_id = free_list_.front();
free_list_.pop_front();
// BUSTUB_ASSERT(frame_id != -1, "");
}else{
} else {
// 最坏情况，去驱除内存页
bool ret = replacer_->Evict(&frame_id);
if(ret == true){ // 驱除成功
if (ret == true) { // 驱除成功
// BUSTUB_ASSERT(frame_id != -1, "");
BUSTUB_ASSERT(pages_[frame_id].GetPinCount() == 0, "");

if(pages_[frame_id].IsDirty()){
if (pages_[frame_id].IsDirty()) {
// 脏页写回磁盘
disk_manager_->WritePage(pages_[frame_id].GetPageId(), pages_[frame_id].GetData());
}
Expand All @@ -85,7 +85,7 @@ auto BufferPoolManager::NewFrameUnlocked(frame_id_t &frame_id) -> Page *{
pages_[frame_id].pin_count_ = 0;
pages_[frame_id].is_dirty_ = false;

}else{
} else {
// 没有多余或者可驱除的frame。
return nullptr;
}
Expand All @@ -101,7 +101,7 @@ auto BufferPoolManager::FetchPage(page_id_t page_id, [[maybe_unused]] AccessType
std::lock_guard<std::mutex> lock(latch_);
auto target = page_table_.find(page_id);
frame_id_t frame_id = -1;
if(target != page_table_.end()){
if (target != page_table_.end()) {
// page在内存中
frame_id = target->second;

Expand All @@ -111,9 +111,9 @@ auto BufferPoolManager::FetchPage(page_id_t page_id, [[maybe_unused]] AccessType
pages_[frame_id].pin_count_++; // 引用计数加一

//return pages_ + frame_id;
}else{
} else {
// page不在内存中
if(NewFrameUnlocked(frame_id) == nullptr) return nullptr; // 缓存满
if (NewFrameUnlocked(frame_id) == nullptr) return nullptr; // 缓存满

replacer_->RecordAccess(frame_id); // 确保frame存在于replacer中，并添加一条history
replacer_->SetEvictable(frame_id, false);
Expand Down Expand Up @@ -141,7 +141,7 @@ auto BufferPoolManager::UnpinPage(page_id_t page_id, bool is_dirty, [[maybe_unus
auto target = page_table_.find(page_id);

//合法性判断
if(target == page_table_.end() || pages_[target->second].GetPinCount() == 0){
if (target == page_table_.end() || pages_[target->second].GetPinCount() == 0) {
return false;
}
frame_id_t frame_id = target->second;
Expand All @@ -150,11 +150,11 @@ auto BufferPoolManager::UnpinPage(page_id_t page_id, bool is_dirty, [[maybe_unus
pages_[frame_id].pin_count_--;
BUSTUB_ASSERT(pages_[frame_id].GetPinCount() >= 0, "");

if(pages_[frame_id].GetPinCount() == 0){
if (pages_[frame_id].GetPinCount() == 0) {
replacer_->SetEvictable(frame_id, true);
}

if(is_dirty == true){
if (is_dirty == true) {
pages_[frame_id].is_dirty_ = true;
}
return true;;
Expand All @@ -164,7 +164,7 @@ auto BufferPoolManager::FlushPage(page_id_t page_id) -> bool {
std::lock_guard<std::mutex> lock(latch_);
auto target = page_table_.find(page_id);

if(target == page_table_.end()){
if (target == page_table_.end()) {
// page 不在内存中
return false;
}
Expand All @@ -183,7 +183,7 @@ auto BufferPoolManager::FlushPage(page_id_t page_id) -> bool {
void BufferPoolManager::FlushAllPages() {
std::lock_guard<std::mutex> lock(latch_);

for(const auto & it : page_table_){
for (const auto & it : page_table_) {
page_id_t page_id = it.first;
frame_id_t frame_id = it.second;

Expand All @@ -201,21 +201,21 @@ auto BufferPoolManager::DeletePage(page_id_t page_id) -> bool {

auto target = page_table_.find(page_id);

if(target == page_table_.end()){
if (target == page_table_.end()) {
// page 不在内存中
return true;
}


if(pages_[target->second].GetPinCount() > 0){
if (pages_[target->second].GetPinCount() > 0) {
return false;
}
frame_id_t frame_id = target->second;
// 确定该page可以删除
BUSTUB_ASSERT(page_id == pages_[frame_id].GetPageId(), "");
BUSTUB_ASSERT(pages_[frame_id].GetPinCount() == 0, "");

if(pages_[frame_id].is_dirty_ == true){
if (pages_[frame_id].is_dirty_ == true) {
// 脏页写回磁盘
disk_manager_->WritePage(page_id, pages_[frame_id].GetData());
}
Expand Down
51 changes: 28 additions & 23 deletions src/buffer/lru_k_replacer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,35 +20,40 @@ LRUKReplacer::LRUKReplacer(size_t num_frames, size_t k) : replacer_size_(num_fra
auto LRUKReplacer::Evict(frame_id_t *frame_id) -> bool {
std::lock_guard<std::mutex> lock(latch_);
auto target = node_store_.end();
size_t targetBKDist = 0;
if(node_store_.empty()){ // 没有可Evict的帧
size_t target_dist_diff = 0;
if (node_store_.empty()) { // 没有可Evict的帧
return false;
}

for(auto it = node_store_.begin(); it != node_store_.end(); it++){
for(auto it = node_store_.begin(); it != node_store_.end(); it++) {
const LRUKNode& node = it->second;
size_t bKDist = 0;
if(node.is_evictable_ == false)
size_t diff_dist = 0;
if (node.is_evictable_ == false)
continue;

if(node.history_.size() == node.k_){ // 记录了k次历史
bKDist = current_timestamp_ - node.history_.back(); // 和前k次时间戳做差
}else{ // 访问不足k次。
bKDist = UINT64_MAX;
if (node.history_.size() == node.k_) { // 记录了k次历史
diff_dist = current_timestamp_ - node.history_.back(); // 和前k次时间戳做差
} else { // 访问不足k次。
diff_dist = UINT64_MAX;
}

if(targetBKDist < bKDist){ // 找到间隔更久的node
if (target_dist_diff < diff_dist) { // 找到间隔更久的node
target = it;
targetBKDist = bKDist;
}else if(targetBKDist == bKDist){ // 相等就比较第kth个时间戳。
if(target->second.history_.back() > node.history_.back()){
target_dist_diff = diff_dist;
} else if (target_dist_diff == diff_dist) { // 相等就比较第kth个时间戳。
if (target->second.history_.empty()) {
// 为空代表存在一个无限小的时间戳
// 既然都无限小了，所以就没有更小的时间戳了
// continue即可。
continue;
} else if (node.history_.empty() || (target->second.history_.back() > node.history_.back())) {
target = it;
targetBKDist = bKDist;
target_dist_diff = diff_dist;
}
}
}

if(target == node_store_.end()){ // 找不到要剔除的frame
if (target == node_store_.end()) { // 找不到要剔除的frame
return false;
}
BUSTUB_ASSERT(target->second.is_evictable_ == true, "is_evictable_ == false!");
Expand All @@ -65,7 +70,7 @@ void LRUKReplacer::RecordAccess(frame_id_t frame_id, [[maybe_unused]] AccessType
BUSTUB_ASSERT((frame_id != -1) && (frame_id < (frame_id_t)replacer_size_), "");

auto target = node_store_.find(frame_id);
if(target == node_store_.end()){ // 没有
if (target == node_store_.end()) { // 没有
target = node_store_.insert(std::make_pair(frame_id, LRUKNode())).first;
target->second.fid_ = frame_id;
target->second.is_evictable_ = false;
Expand All @@ -75,9 +80,9 @@ void LRUKReplacer::RecordAccess(frame_id_t frame_id, [[maybe_unused]] AccessType
BUSTUB_ASSERT(curr_size_ <= replacer_size_, "");
}
// need mark to is_evictable_ == false?
if(target->second.history_.size() < target->second.k_){
if (target->second.history_.size() < target->second.k_) {
target->second.history_.push_front(++current_timestamp_);
}else{ // ==
} else { // ==
BUSTUB_ASSERT(target->second.history_.size() == target->second.k_, "");
target->second.history_.push_front(++current_timestamp_);
target->second.history_.pop_back();
Expand All @@ -90,17 +95,17 @@ void LRUKReplacer::SetEvictable(frame_id_t frame_id, bool set_evictable) {

auto target = node_store_.find(frame_id);

if(target != node_store_.end()){
if(target->second.is_evictable_ == true && set_evictable == false){
if (target != node_store_.end()) {
if (target->second.is_evictable_ == true && set_evictable == false) {
target->second.is_evictable_ = false;
BUSTUB_ASSERT(curr_size_ - 1 < curr_size_, "");
curr_size_--;
}else if(target->second.is_evictable_ == false && set_evictable == true){
} else if (target->second.is_evictable_ == false && set_evictable == true) {
target->second.is_evictable_ = true;
curr_size_++;
BUSTUB_ASSERT(curr_size_ <= replacer_size_, "");
}
}else{// 什么也不做
} else {// 什么也不做
BUSTUB_ASSERT(false, "");
}
// 考虑可以自学习？
Expand All @@ -111,7 +116,7 @@ void LRUKReplacer::Remove(frame_id_t frame_id) {
BUSTUB_ASSERT(frame_id < (frame_id_t)replacer_size_, "");

auto target = node_store_.find(frame_id);
if(target != node_store_.end()){
if (target != node_store_.end()) {
BUSTUB_ASSERT(target->second.is_evictable_ == true, "");
node_store_.erase(target);
BUSTUB_ASSERT(curr_size_ - 1 < curr_size_, "");
Expand Down
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