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/manager.go

@@ -0,0 +1,216 @@
+package memtable
+
+import (
+	"sync"
+)
+
+// ImmutableMemTable 不可变的 MemTable
+type ImmutableMemTable struct {
+	MemTable  *MemTable
+	WALNumber int64 // 对应的 WAL 编号
+}
+
+// Manager MemTable 管理器
+type Manager struct {
+	active     *MemTable            // Active MemTable (可写)
+	immutables []*ImmutableMemTable // Immutable MemTables (只读)
+	activeWAL  int64                // Active MemTable 对应的 WAL 编号
+	maxSize    int64                // MemTable 最大大小
+	mu         sync.RWMutex         // 读写锁
+}
+
+// NewManager 创建 MemTable 管理器
+func NewManager(maxSize int64) *Manager {
+	return &Manager{
+		active:     New(),
+		immutables: make([]*ImmutableMemTable, 0),
+		maxSize:    maxSize,
+	}
+}
+
+// SetActiveWAL 设置 Active MemTable 对应的 WAL 编号
+func (m *Manager) SetActiveWAL(walNumber int64) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.activeWAL = walNumber
+}
+
+// Put 写入数据到 Active MemTable
+func (m *Manager) Put(key int64, value []byte) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.active.Put(key, value)
+}
+
+// Get 查询数据（先查 Active，再查 Immutables）
+func (m *Manager) Get(key int64) ([]byte, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	// 1. 先查 Active MemTable
+	if value, found := m.active.Get(key); found {
+		return value, true
+	}
+
+	// 2. 查 Immutable MemTables（从新到旧）
+	for i := len(m.immutables) - 1; i >= 0; i-- {
+		if value, found := m.immutables[i].MemTable.Get(key); found {
+			return value, true
+		}
+	}
+
+	return nil, false
+}
+
+// GetActiveSize 获取 Active MemTable 大小
+func (m *Manager) GetActiveSize() int64 {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.active.Size()
+}
+
+// GetActiveCount 获取 Active MemTable 条目数
+func (m *Manager) GetActiveCount() int {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.active.Count()
+}
+
+// ShouldSwitch 检查是否需要切换 MemTable
+func (m *Manager) ShouldSwitch() bool {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.active.Size() >= m.maxSize
+}
+
+// Switch 切换 MemTable（Active → Immutable，创建新 Active）
+// 返回：旧的 WAL 编号，新的 Active MemTable
+func (m *Manager) Switch(newWALNumber int64) (oldWALNumber int64, immutable *ImmutableMemTable) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	// 1. 将 Active 变为 Immutable
+	immutable = &ImmutableMemTable{
+		MemTable:  m.active,
+		WALNumber: m.activeWAL,
+	}
+	m.immutables = append(m.immutables, immutable)
+
+	// 2. 创建新的 Active MemTable
+	m.active = New()
+	oldWALNumber = m.activeWAL
+	m.activeWAL = newWALNumber
+
+	return oldWALNumber, immutable
+}
+
+// RemoveImmutable 移除指定的 Immutable MemTable
+func (m *Manager) RemoveImmutable(target *ImmutableMemTable) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	// 查找并移除
+	for i, imm := range m.immutables {
+		if imm == target {
+			m.immutables = append(m.immutables[:i], m.immutables[i+1:]...)
+			break
+		}
+	}
+}
+
+// GetImmutableCount 获取 Immutable MemTable 数量
+func (m *Manager) GetImmutableCount() int {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return len(m.immutables)
+}
+
+// GetImmutables 获取所有 Immutable MemTables（副本）
+func (m *Manager) GetImmutables() []*ImmutableMemTable {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	immutables := make([]*ImmutableMemTable, len(m.immutables))
+	copy(immutables, m.immutables)
+	return immutables
+}
+
+// GetActive 获取 Active MemTable（用于 Flush 时读取）
+func (m *Manager) GetActive() *MemTable {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.active
+}
+
+// TotalCount 获取总条目数（Active + Immutables）
+func (m *Manager) TotalCount() int {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	total := m.active.Count()
+	for _, imm := range m.immutables {
+		total += imm.MemTable.Count()
+	}
+	return total
+}
+
+// TotalSize 获取总大小（Active + Immutables）
+func (m *Manager) TotalSize() int64 {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	total := m.active.Size()
+	for _, imm := range m.immutables {
+		total += imm.MemTable.Size()
+	}
+	return total
+}
+
+// NewIterator 创建 Active MemTable 的迭代器
+func (m *Manager) NewIterator() *Iterator {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	return m.active.NewIterator()
+}
+
+// Stats 统计信息
+type Stats struct {
+	ActiveSize      int64
+	ActiveCount     int
+	ImmutableCount  int
+	ImmutablesSize  int64
+	ImmutablesTotal int
+	TotalSize       int64
+	TotalCount      int
+}
+
+// GetStats 获取统计信息
+func (m *Manager) GetStats() *Stats {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	stats := &Stats{
+		ActiveSize:     m.active.Size(),
+		ActiveCount:    m.active.Count(),
+		ImmutableCount: len(m.immutables),
+	}
+
+	for _, imm := range m.immutables {
+		stats.ImmutablesSize += imm.MemTable.Size()
+		stats.ImmutablesTotal += imm.MemTable.Count()
+	}
+
+	stats.TotalSize = stats.ActiveSize + stats.ImmutablesSize
+	stats.TotalCount = stats.ActiveCount + stats.ImmutablesTotal
+
+	return stats
+}
+
+// Clear 清空所有 MemTables（用于测试）
+func (m *Manager) Clear() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	m.active = New()
+	m.immutables = make([]*ImmutableMemTable, 0)
+}