feat(core): optimize performance and reliability through batching and redis-backed unread counts

This commit introduces several significant architectural improvements to enhance system performance, scalability, and reliability:

- **Performance Optimization (N+1 Problem Resolution)**: Implemented batching mechanisms across `MessageHandler`, `ChatService`, `GroupService`, `MessageService`, and `UserService`. This replaces multiple individual database/cache queries with single batch operations for fetching unread counts, last messages, participants, and user information.
- **Enhanced Unread Count Management**: Migrated unread count tracking to a Redis Hash-based approach (`unread#️⃣{userID}`). This allows for atomic increments/decrements and efficient retrieval of both individual conversation unread counts and total unread counts for a user.
- **Improved Message Sequencing**: Integrated Redis-based sequence (`seq`) pre-allocation for messages to ensure strict ordering and reduce database contention during high-concurrency message creation.
- **Push Service Reliability**: Refactored the push notification system to include persistent `PushRecord` tracking. Added a recovery mechanism (`recoverPendingPushes`) to reload pending notifications from the database upon service startup, ensuring better delivery guarantees.
- **WebSocket Reliability**: Updated the WebSocket hub to move away from in-memory history replay in favor of a client-driven synchronization model (`sync_required` event and `ack` handling), reducing memory overhead and improving connection stability.
- **Cache Layer Enhancements**: Added `HIncrBy` and `IncrBySeq` to the `Cache` interface and its implementations (`RedisCache`, `LayeredCache`) to support the new unread and sequence management logic.

internal/service/chat_service.go

@@ -56,6 +56,10 @@ type ChatService interface {
 
 	// 仅保存消息到数据库，不发送实时推送（供群聊等自行推送的场景使用）
 	SaveMessage(ctx context.Context, senderID string, conversationID string, segments model.MessageSegments, replyToID *string) (*model.Message, error)
+
+	// 批量查询（解决 N+1 问题）
+	GetUnreadCountBatch(ctx context.Context, userID string, convIDs []string) (map[string]int64, error)
+	GetLastMessagesBatch(ctx context.Context, convIDs []string) (map[string]*model.Message, error)
 }
 
 // chatServiceImpl 聊天服务实现
@@ -333,6 +337,19 @@ func (s *chatServiceImpl) SendMessage(ctx context.Context, senderID string, conv
 		Status:         model.MessageStatusNormal,
 	}
 
+	// 从 Redis 获取下一个 seq
+	if s.conversationCache != nil {
+		seq, err := s.conversationCache.GetNextSeq(ctx, conversationID)
+		if err != nil {
+			zap.L().Warn("redis get next seq failed, falling back to DB",
+				zap.String("convID", conversationID),
+				zap.Error(err),
+			)
+		} else {
+			message.Seq = seq
+		}
+	}
+
 	// 使用事务创建消息并更新seq
 	if err := s.repo.CreateMessageWithSeq(message); err != nil {
 		return nil, fmt.Errorf("failed to save message: %w", err)
@@ -397,6 +414,20 @@ func (s *chatServiceImpl) SendMessage(ctx context.Context, senderID string, conv
 	}
 
 	if s.conversationCache != nil {
+		// 使用 Redis Hash 预计算未读数
+		for _, p := range participants {
+			if p.UserID == senderID {
+				continue
+			}
+			if incrErr := s.conversationCache.IncrementUnread(context.Background(), p.UserID, conversationID); incrErr != nil {
+				zap.L().Warn("increment unread from redis hash failed",
+					zap.String("userID", p.UserID),
+					zap.String("convID", conversationID),
+					zap.Error(incrErr),
+				)
+			}
+		}
+
 		keys := make([]string, 0, len(participants)*2)
 		for _, p := range participants {
 			keys = append(keys,
@@ -559,11 +590,18 @@ func (s *chatServiceImpl) MarkAsRead(ctx context.Context, conversationID string,
 		return fmt.Errorf("failed to update last read seq: %w", err)
 	}
 
-	// 2. DB 写入成功后，失效缓存（Cache-Aside 模式）
+	// 2. DB 写入成功后，清除 Redis 未读数
 	if s.conversationCache != nil {
+		if clearErr := s.conversationCache.ClearUnread(ctx, userID, conversationID); clearErr != nil {
+			zap.L().Warn("clear unread from redis hash failed",
+				zap.String("userID", userID),
+				zap.String("convID", conversationID),
+				zap.Error(clearErr),
+			)
+		}
 		// 失效参与者缓存，下次读取时会从 DB 加载最新数据
 		s.conversationCache.InvalidateParticipant(conversationID, userID)
-		// 失效未读数缓存
+		// 失效未读数缓存（旧 cache-aside 键）
 		s.conversationCache.InvalidateUnreadCount(userID, conversationID)
 		// 失效会话列表缓存
 		s.conversationCache.InvalidateConversationList(userID)
@@ -612,8 +650,13 @@ func (s *chatServiceImpl) GetUnreadCount(ctx context.Context, conversationID str
 		return 0, fmt.Errorf("failed to get participant: %w", err)
 	}
 
-	// 优先使用缓存
+	// 优先从 Redis Hash 读取
 	if s.conversationCache != nil {
+		count, err := s.conversationCache.GetUnreadCountFromHash(ctx, userID, conversationID)
+		if err == nil {
+			return count, nil
+		}
+		// 降级到旧缓存路径
 		return s.conversationCache.GetUnreadCount(ctx, userID, conversationID)
 	}
 
@@ -622,6 +665,12 @@ func (s *chatServiceImpl) GetUnreadCount(ctx context.Context, conversationID str
 
 // GetAllUnreadCount 获取所有会话的未读消息总数
 func (s *chatServiceImpl) GetAllUnreadCount(ctx context.Context, userID string) (int64, error) {
+	// 优先从 Redis Hash 读取
+	if s.conversationCache != nil {
+		if total, err := s.conversationCache.GetTotalUnread(ctx, userID); err == nil {
+			return total, nil
+		}
+	}
 	return s.repo.GetAllUnreadCount(userID)
 }
 
@@ -798,6 +847,19 @@ func (s *chatServiceImpl) SaveMessage(ctx context.Context, senderID string, conv
 		Status:         model.MessageStatusNormal,
 	}
 
+	// 从 Redis 获取下一个 seq（SaveMessage 方法）
+	if s.conversationCache != nil {
+		seq, err := s.conversationCache.GetNextSeq(ctx, conversationID)
+		if err != nil {
+			zap.L().Warn("redis get next seq failed, falling back to DB",
+				zap.String("convID", conversationID),
+				zap.Error(err),
+			)
+		} else {
+			message.Seq = seq
+		}
+	}
+
 	if err := s.repo.CreateMessageWithSeq(message); err != nil {
 		return nil, fmt.Errorf("failed to save message: %w", err)
 	}
@@ -821,3 +883,13 @@ func (s *chatServiceImpl) SaveMessage(ctx context.Context, senderID string, conv
 
 	return message, nil
 }
+
+// GetUnreadCountBatch 批量获取用户在多个会话中的未读数
+func (s *chatServiceImpl) GetUnreadCountBatch(ctx context.Context, userID string, convIDs []string) (map[string]int64, error) {
+	return s.repo.GetUnreadCountBatch(ctx, userID, convIDs)
+}
+
+// GetLastMessagesBatch 批量获取每个会话的最后一条消息
+func (s *chatServiceImpl) GetLastMessagesBatch(ctx context.Context, convIDs []string) (map[string]*model.Message, error) {
+	return s.repo.GetLastMessagesBatch(ctx, convIDs)
+}