Initial commit: SRDB - High-performance LSM-Tree database

- Core engine with MemTable, SST, WAL
- B+Tree indexing for SST files  
- Leveled compaction strategy
- Multi-table database management
- Schema validation and secondary indexes
- Query builder with complex conditions
- Web UI with HTMX for data visualization
- Command-line tools for diagnostics

btree/reader.go

@@ -0,0 +1,106 @@
+package btree
+
+import (
+	"sort"
+
+	"github.com/edsrzf/mmap-go"
+)
+
+// Reader 用于查询 B+Tree (mmap)
+type Reader struct {
+	mmap       mmap.MMap
+	rootOffset int64
+}
+
+// NewReader 创建查询器
+func NewReader(mmap mmap.MMap, rootOffset int64) *Reader {
+	return &Reader{
+		mmap:       mmap,
+		rootOffset: rootOffset,
+	}
+}
+
+// Get 查询 key，返回数据位置
+func (r *Reader) Get(key int64) (dataOffset int64, dataSize int32, found bool) {
+	if r.rootOffset == 0 {
+		return 0, 0, false
+	}
+
+	nodeOffset := r.rootOffset
+
+	for {
+		// 读取节点 (零拷贝)
+		if nodeOffset+NodeSize > int64(len(r.mmap)) {
+			return 0, 0, false
+		}
+
+		nodeData := r.mmap[nodeOffset : nodeOffset+NodeSize]
+		node := Unmarshal(nodeData)
+
+		if node == nil {
+			return 0, 0, false
+		}
+
+		// 叶子节点
+		if node.NodeType == NodeTypeLeaf {
+			// 二分查找
+			idx := sort.Search(len(node.Keys), func(i int) bool {
+				return node.Keys[i] >= key
+			})
+			if idx < len(node.Keys) && node.Keys[idx] == key {
+				return node.DataOffsets[idx], node.DataSizes[idx], true
+			}
+			return 0, 0, false
+		}
+
+		// 内部节点，继续向下
+		// keys[i] 是分隔符，children[i] 包含 < keys[i] 的数据
+		// children[i+1] 包含 >= keys[i] 的数据
+		idx := sort.Search(len(node.Keys), func(i int) bool {
+			return node.Keys[i] > key
+		})
+		// idx 现在指向第一个 > key 的位置
+		// 我们应该走 children[idx]
+		if idx >= len(node.Children) {
+			idx = len(node.Children) - 1
+		}
+		nodeOffset = node.Children[idx]
+	}
+}
+
+// GetAllKeys 获取 B+Tree 中所有的 key（按顺序）
+func (r *Reader) GetAllKeys() []int64 {
+	if r.rootOffset == 0 {
+		return nil
+	}
+
+	var keys []int64
+	r.traverseLeafNodes(r.rootOffset, func(node *BTreeNode) {
+		keys = append(keys, node.Keys...)
+	})
+	return keys
+}
+
+// traverseLeafNodes 遍历所有叶子节点
+func (r *Reader) traverseLeafNodes(nodeOffset int64, callback func(*BTreeNode)) {
+	if nodeOffset+NodeSize > int64(len(r.mmap)) {
+		return
+	}
+
+	nodeData := r.mmap[nodeOffset : nodeOffset+NodeSize]
+	node := Unmarshal(nodeData)
+
+	if node == nil {
+		return
+	}
+
+	if node.NodeType == NodeTypeLeaf {
+		// 叶子节点，执行回调
+		callback(node)
+	} else {
+		// 内部节点，递归遍历所有子节点
+		for _, childOffset := range node.Children {
+			r.traverseLeafNodes(childOffset, callback)
+		}
+	}
+}