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

memtable/memtable.go

@@ -0,0 +1,141 @@
+package memtable
+
+import (
+	"sort"
+	"sync"
+)
+
+// MemTable 内存表
+type MemTable struct {
+	data map[int64][]byte // key -> value
+	keys []int64          // 排序的 keys
+	size int64            // 数据大小
+	mu   sync.RWMutex
+}
+
+// New 创建 MemTable
+func New() *MemTable {
+	return &MemTable{
+		data: make(map[int64][]byte),
+		keys: make([]int64, 0),
+		size: 0,
+	}
+}
+
+// Put 插入数据
+func (m *MemTable) Put(key int64, value []byte) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	// 检查是否已存在
+	if _, exists := m.data[key]; !exists {
+		m.keys = append(m.keys, key)
+		// 保持 keys 有序
+		sort.Slice(m.keys, func(i, j int) bool {
+			return m.keys[i] < m.keys[j]
+		})
+	}
+
+	m.data[key] = value
+	m.size += int64(len(value))
+}
+
+// Get 查询数据
+func (m *MemTable) Get(key int64) ([]byte, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	value, exists := m.data[key]
+	return value, exists
+}
+
+// Size 获取大小
+func (m *MemTable) Size() int64 {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	return m.size
+}
+
+// Count 获取条目数量
+func (m *MemTable) Count() int {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	return len(m.data)
+}
+
+// Keys 获取所有 keys 的副本（已排序）
+func (m *MemTable) Keys() []int64 {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	// 返回副本以避免并发问题
+	keysCopy := make([]int64, len(m.keys))
+	copy(keysCopy, m.keys)
+	return keysCopy
+}
+
+// Iterator 迭代器
+type Iterator struct {
+	mt    *MemTable
+	index int
+}
+
+// NewIterator 创建迭代器
+func (m *MemTable) NewIterator() *Iterator {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	return &Iterator{
+		mt:    m,
+		index: -1,
+	}
+}
+
+// Next 移动到下一个
+func (it *Iterator) Next() bool {
+	it.mt.mu.RLock()
+	defer it.mt.mu.RUnlock()
+
+	it.index++
+	return it.index < len(it.mt.keys)
+}
+
+// Key 当前 key
+func (it *Iterator) Key() int64 {
+	it.mt.mu.RLock()
+	defer it.mt.mu.RUnlock()
+
+	if it.index < 0 || it.index >= len(it.mt.keys) {
+		return 0
+	}
+	return it.mt.keys[it.index]
+}
+
+// Value 当前 value
+func (it *Iterator) Value() []byte {
+	it.mt.mu.RLock()
+	defer it.mt.mu.RUnlock()
+
+	if it.index < 0 || it.index >= len(it.mt.keys) {
+		return nil
+	}
+	key := it.mt.keys[it.index]
+	return it.mt.data[key]
+}
+
+// Reset 重置迭代器
+func (it *Iterator) Reset() {
+	it.index = -1
+}
+
+// Clear 清空 MemTable
+func (m *MemTable) Clear() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	m.data = make(map[int64][]byte)
+	m.keys = make([]int64, 0)
+	m.size = 0
+}