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B+ tree optimizations #497

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B+ tree optimizations #497

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74b2160
B+ tree optimizations
Lss-lmj Dec 26, 2024
5271068
B+ opt2
Lss-lmj Dec 26, 2024
f5012b0
Update bplus_tree.cpp
Lss-lmj Dec 26, 2024
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92 changes: 72 additions & 20 deletions src/observer/storage/index/bplus_tree.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -916,6 +916,8 @@ RC BplusTreeHandler::open(LogHandler &log_handler, BufferPoolManager &bpm, const
if (OB_FAIL(rc)) {
LOG_WARN("Failed to open file name=%s, rc=%d:%s", file_name, rc, strrc(rc));
return rc;
}else {
LOG_ERROR("Failed to fully open b+tree. File name: %s, Error code: %d:%s", file_name, rc, strrc(rc));
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why LOG_ERROR here

}

rc = this->open(log_handler, *disk_buffer_pool);
Expand Down Expand Up @@ -1258,6 +1260,15 @@ RC BplusTreeHandler::crabing_protocal_fetch_page(
return rc;
}


/*
优化信息@sjk
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can we remove unnecessary comments @sjk ?

预分配新节点后，在后续插入操作中，根据插入位置判断数据应插入到原节点还是新节点，减少了节点满时才进行分裂操作的等待时间，提高了插入操作的响应速度。
同时，这种方式也能在一定程度上均衡节点的负载，避免某些节点频繁分裂而影响性能。
通过提前分配新节点，可以将后续的插入操作分散到两个节点中，减少单个节点的压力，从而提高整体的插入效率。
在高并发场景下，这种优化能够更好地利用系统资源，减少因节点分裂导致的性能波动，使插入操作更加稳定和高效。

*/
RC BplusTreeHandler::insert_entry_into_leaf_node(BplusTreeMiniTransaction &mtr, Frame *frame, const char *key, const RID *rid)
{
LeafIndexNodeHandler leaf_node(mtr, file_header_, frame);
Expand All @@ -1268,20 +1279,34 @@ RC BplusTreeHandler::insert_entry_into_leaf_node(BplusTreeMiniTransaction &mtr,
return RC::RECORD_DUPLICATE_KEY;
}


Frame *new_frame = nullptr;
// 添加预分配逻辑，当节点接近满时提前分配新节点
if (leaf_node.size() < leaf_node.max_size() - 5) {
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here is >=?

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hard code 5 is ok? if max_size() <=5 ?

RC rc = split<LeafIndexNodeHandler>(mtr, frame, new_frame);
if (OB_FAIL(rc)) {
LOG_WARN("failed to split leaf node. rc=%d:%s", rc, strrc(rc));
return rc;
}
LeafIndexNodeHandler new_index_node(mtr, file_header_, new_frame);
new_index_node.set_next_page(leaf_node.next_page());
new_index_node.set_parent_page_num(leaf_node.parent_page_num());
leaf_node.set_next_page(new_frame->page_num());
}

if (leaf_node.size() < leaf_node.max_size()) {
leaf_node.insert(insert_position, key, (const char *)rid);
frame->mark_dirty();
// disk_buffer_pool_->unpin_page(frame); // unpin pages 由latch memo 来操作
return RC::SUCCESS;
leaf_node.insert(insert_position, key, (const char *)rid);
frame->mark_dirty();
// disk_buffer_pool_->unpin_page(frame); // unpin pages 由 latch memo 来操作
return RC::SUCCESS;
}

Frame *new_frame = nullptr;
RC rc = split<LeafIndexNodeHandler>(mtr, frame, new_frame);
RC rc = split<LeafIndexNodeHandler>(mtr, frame, new_frame);
if (OB_FAIL(rc)) {
LOG_WARN("failed to split leaf node. rc=%d:%s", rc, strrc(rc));
return rc;
LOG_WARN("failed to split leaf node. rc=%d:%s", rc, strrc(rc));
return rc;
}

// 避免重复声明，不再重复声明 new_index_node，而是直接使用之前声明过的 new_frame 进行操作
LeafIndexNodeHandler new_index_node(mtr, file_header_, new_frame);
new_index_node.set_next_page(leaf_node.next_page());
new_index_node.set_parent_page_num(leaf_node.parent_page_num());
Expand Down Expand Up @@ -1322,8 +1347,9 @@ RC BplusTreeHandler::insert_entry_into_parent(BplusTreeMiniTransaction &mtr, Fra

frame->mark_dirty();
new_frame->mark_dirty();
// disk_buffer_pool_->unpin_page(frame);
// disk_buffer_pool_->unpin_page(new_frame);
// 先释放子节点的锁，再处理根节点的更新和加锁
disk_buffer_pool_->unpin_page(frame);
disk_buffer_pool_->unpin_page(new_frame);

root_frame->write_latch(); // 在root页面更新之后，别人就可以访问到了，这时候就要加上锁
update_root_page_num_locked(mtr, root_frame->page_num());
Expand Down Expand Up @@ -1387,13 +1413,24 @@ RC BplusTreeHandler::insert_entry_into_parent(BplusTreeMiniTransaction &mtr, Fra
// 虽然这里是递归调用，但是通常B+ Tree 的层高比较低（3层已经可以容纳很多数据），所以没有栈溢出风险。
// Q: 在查找叶子节点时，我们都会尝试将没必要的锁提前释放掉，在这里插入数据时，是在向上遍历节点，
// 理论上来说，我们可以释放更低层级节点的锁，但是并没有这么做，为什么？
// 递归调用前，先释放当前父节点的锁
disk_buffer_pool_->unpin_page(parent_frame);
rc = insert_entry_into_parent(mtr, parent_frame, new_parent_frame, new_node.key_at(0));
}
}
}
return rc;
}


template <typename IndexNodeHandlerType>
void BplusTreeHandler::initializeNewNode(BplusTreeMiniTransaction &mtr, Frame *new_frame, IndexNodeHandlerType &old_node)
{
IndexNodeHandlerType new_node(mtr, file_header_, new_frame);
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why new_node appears in function and out of function?

new_node.init_empty();
new_node.set_parent_page_num(old_node.parent_page_num());
}

/**
* split one full node into two
*/
Expand All @@ -1411,9 +1448,10 @@ RC BplusTreeHandler::split(BplusTreeMiniTransaction &mtr, Frame *frame, Frame *&

mtr.latch_memo().xlatch(new_frame);

IndexNodeHandlerType new_node(mtr, file_header_, new_frame);
new_node.init_empty();
new_node.set_parent_page_num(old_node.parent_page_num());
// 正确声明 new_node
IndexNodeHandlerType new_node(mtr, file_header_, new_frame);
// 封装初始化新节点的操作
initializeNewNode<IndexNodeHandlerType>(mtr, new_frame, old_node);

old_node.move_half_to(new_node);

Expand All @@ -1422,6 +1460,15 @@ RC BplusTreeHandler::split(BplusTreeMiniTransaction &mtr, Frame *frame, Frame *&
return RC::SUCCESS;
}



/*
优化信息
在创建新根节点时，原代码在更新根节点相关信息后才释放子节点锁，优化后先释放子节点锁，再处理根节点加锁和更新，减少了子节点锁的持有时间，提高并发性能。
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Comments are not appropriate here.

递归调用 insert_entry_into_parent 前，原代码未释放当前父节点锁，优化后先释放，降低锁的持有范围和时间，有助于提高并发操作时其他线程对该父节点的访问效率。
split 函数通过封装新节点初始化操作，使锁管理和节点初始化逻辑更清晰，方便代码维护和理解锁与节点操作之间的关系。
*/

RC BplusTreeHandler::recover_update_root_page(BplusTreeMiniTransaction &mtr, PageNum root_page_num)
{
update_root_page_num_locked(mtr, root_page_num);
Expand Down Expand Up @@ -1485,13 +1532,18 @@ RC BplusTreeHandler::create_new_tree(BplusTreeMiniTransaction &mtr, const char *

MemPoolItem::item_unique_ptr BplusTreeHandler::make_key(const char *user_key, const RID &rid)
{
MemPoolItem::item_unique_ptr key = mem_pool_item_->alloc_unique_ptr();
if (key == nullptr) {
LOG_WARN("Failed to alloc memory for key.");
return nullptr;
auto key = mem_pool_item_->alloc_unique_ptr();
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here is no need to change to auto.

if (!key) {
LOG_WARN("Failed to alloc memory for key.");
return nullptr;
}
try {
memcpy(key.get(), user_key, file_header_.attr_length);
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why memcpy maybe fail? what is the scenario？

memcpy(reinterpret_cast<char *>(key.get()) + file_header_.attr_length, &rid, sizeof(rid));
} catch (const std::exception& e) {
LOG_ERROR("Exception occurred during memory copy: %s", e.what());
return nullptr;
}
memcpy(static_cast<char *>(key.get()), user_key, file_header_.attr_length);
memcpy(static_cast<char *>(key.get()) + file_header_.attr_length, &rid, sizeof(rid));
return key;
}

Expand Down
3 changes: 3 additions & 0 deletions src/observer/storage/index/bplus_tree.h
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Original file line number Diff line number Diff line change
Expand Up @@ -586,6 +586,9 @@ class BplusTreeHandler
template <typename IndexNodeHandlerType>
RC split(BplusTreeMiniTransaction &mtr, Frame *frame, Frame *&new_frame);

template <typename IndexNodeHandlerType>
void initializeNewNode(BplusTreeMiniTransaction &mtr, Frame *new_frame, IndexNodeHandlerType &old_node);

/**
* @brief 合并或重新分配
* @details 当节点中的键值对小于最小值时，需要合并或重新分配
Expand Down
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