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/repository/group_repo.go

@@ -27,6 +27,7 @@ type GroupRepository interface {
 	UpdateMember(member *model.GroupMember) error
 	RemoveMember(groupID string, userID string) error
 	GetMemberCount(groupID string) (int64, error)
+	GetMemberCountBatch(ctx context.Context, groupIDs []string) (map[string]int64, error)
 	IsMember(groupID string, userID string) (bool, error)
 	GetUserGroups(userID string, page, pageSize int) ([]model.Group, int64, error)
 
@@ -225,6 +226,34 @@ func (r *groupRepository) GetMemberCount(groupID string) (int64, error) {
 	return count, err
 }
 
+// GetMemberCountBatch 批量获取多个群的成员数量
+func (r *groupRepository) GetMemberCountBatch(ctx context.Context, groupIDs []string) (map[string]int64, error) {
+	result := make(map[string]int64, len(groupIDs))
+	if len(groupIDs) == 0 {
+		return result, nil
+	}
+
+	type row struct {
+		GroupID     string
+		Count       int64
+	}
+	var rows []row
+	err := r.db.WithContext(ctx).
+		Model(&model.GroupMember{}).
+		Select("group_id, COUNT(*) as count").
+		Where("group_id IN ?", groupIDs).
+		Group("group_id").
+		Scan(&rows).Error
+	if err != nil {
+		return nil, err
+	}
+
+	for _, r := range rows {
+		result[r.GroupID] = r.Count
+	}
+	return result, nil
+}
+
 // IsMember 检查是否是群成员
 func (r *groupRepository) IsMember(groupID string, userID string) (bool, error) {
 	var count int64

internal/repository/message_repo.go

@@ -54,6 +54,12 @@ type MessageRepository interface {
 	UpdateConversationLastSeqWithTx(tx *gorm.DB, convID string, lastSeq int64, lastMsgTime time.Time) error
 	GetMessagesByCursor(ctx context.Context, conversationID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Message], error)
 	GetConversationsByCursor(ctx context.Context, userID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Conversation], error)
+
+	// 批量查询方法（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)
+	GetParticipantsBatch(ctx context.Context, convIDs []string) (map[string][]*model.ConversationParticipant, error)
+	GetMyParticipantsBatch(ctx context.Context, convIDs []string, userID string) (map[string]*model.ConversationParticipant, error)
 }
 
 // messageRepository 消息仓储实现
@@ -405,17 +411,10 @@ func (r *messageRepository) GetNextSeq(conversationID string) (int64, error) {
 }
 
 // CreateMessageWithSeq 创建消息并更新seq（事务操作）
+// msg.Seq 应由调用方通过 Redis INCR 预分配
 func (r *messageRepository) CreateMessageWithSeq(msg *model.Message) error {
 	return r.db.Transaction(func(tx *gorm.DB) error {
-		// 获取当前seq并+1
-		var conv model.Conversation
-		if err := tx.Select("last_seq").Where("id = ?", msg.ConversationID).First(&conv).Error; err != nil {
-			return err
-		}
-
-		msg.Seq = conv.LastSeq + 1
-
-		// 创建消息
+		// 创建消息（seq 已由调用方预分配）
 		if err := tx.Create(msg).Error; err != nil {
 			return err
 		}
@@ -430,7 +429,7 @@ func (r *messageRepository) CreateMessageWithSeq(msg *model.Message) error {
 			return err
 		}
 
-		// 新消息到达后，自动恢复被“仅自己删除”的会话
+		// 新消息到达后，自动恢复被"仅自己删除"的会话
 		if err := tx.Model(&model.ConversationParticipant{}).
 			Where("conversation_id = ?", msg.ConversationID).
 			Update("hidden_at", nil).Error; err != nil {
@@ -883,3 +882,101 @@ func (r *messageRepository) GetConversationsByCursor(ctx context.Context, userID
 
 	return cursor.NewCursorPageResult(conversations, nextCursor, prevCursor, hasMore), nil
 }
+
+// GetUnreadCountBatch 批量获取用户在多个会话中的未读数
+func (r *messageRepository) GetUnreadCountBatch(ctx context.Context, userID string, convIDs []string) (map[string]int64, error) {
+	result := make(map[string]int64, len(convIDs))
+	if len(convIDs) == 0 {
+		return result, nil
+	}
+
+	type row struct {
+		ConversationID string
+		Count          int64
+	}
+	var rows []row
+	err := r.db.WithContext(ctx).
+		Table("conversation_participants cp").
+		Select("cp.conversation_id, COALESCE(cnt.unread, 0) as count").
+		Joins("LEFT JOIN (SELECT m.conversation_id, COUNT(m.id) as unread FROM messages m WHERE m.sender_id <> ? AND m.deleted_at IS NULL AND m.conversation_id IN (?) GROUP BY m.conversation_id) cnt ON cnt.conversation_id = cp.conversation_id AND cnt.unread > cp.last_read_seq", userID, convIDs).
+		Where("cp.user_id = ? AND cp.conversation_id IN (?)", userID, convIDs).
+		Scan(&rows).Error
+	if err != nil {
+		return nil, err
+	}
+
+	for _, id := range convIDs {
+		result[id] = 0
+	}
+	for _, r := range rows {
+		result[r.ConversationID] = r.Count
+	}
+	return result, nil
+}
+
+// GetLastMessagesBatch 批量获取每个会话的最后一条消息
+func (r *messageRepository) GetLastMessagesBatch(ctx context.Context, convIDs []string) (map[string]*model.Message, error) {
+	result := make(map[string]*model.Message, len(convIDs))
+	if len(convIDs) == 0 {
+		return result, nil
+	}
+
+	var messages []*model.Message
+	err := r.db.WithContext(ctx).
+		Where("id IN (?)", r.db.
+			Select("MAX(id)").
+			Table("messages").
+			Where("conversation_id IN (?) AND deleted_at IS NULL", convIDs).
+			Group("conversation_id")).
+		Find(&messages).Error
+	if err != nil {
+		return nil, err
+	}
+
+	for _, m := range messages {
+		result[m.ConversationID] = m
+	}
+	return result, nil
+}
+
+// GetParticipantsBatch 批量获取多个会话的参与者列表
+func (r *messageRepository) GetParticipantsBatch(ctx context.Context, convIDs []string) (map[string][]*model.ConversationParticipant, error) {
+	result := make(map[string][]*model.ConversationParticipant, len(convIDs))
+	if len(convIDs) == 0 {
+		return result, nil
+	}
+
+	var participants []*model.ConversationParticipant
+	err := r.db.WithContext(ctx).
+		Where("conversation_id IN (?)", convIDs).
+		Find(&participants).Error
+	if err != nil {
+		return nil, err
+	}
+
+	for _, p := range participants {
+		result[p.ConversationID] = append(result[p.ConversationID], p)
+	}
+	return result, nil
+}
+
+// GetMyParticipantsBatch 批量获取用户在多个会话中的参与者信息
+func (r *messageRepository) GetMyParticipantsBatch(ctx context.Context, convIDs []string, userID string) (map[string]*model.ConversationParticipant, error) {
+	result := make(map[string]*model.ConversationParticipant, len(convIDs))
+	if len(convIDs) == 0 {
+		return result, nil
+	}
+
+	var participants []*model.ConversationParticipant
+	err := r.db.WithContext(ctx).
+		Where("conversation_id IN (?) AND user_id = ?", convIDs, userID).
+		Find(&participants).Error
+	if err != nil {
+		return nil, err
+	}
+
+	for _, p := range participants {
+		result[p.ConversationID] = p
+	}
+	return result, nil
+}

internal/repository/user_repo.go

@@ -1,6 +1,7 @@
 package repository
 
 import (
+	"context"
 	"strings"
 	"time"
 	"with_you/internal/model"
@@ -13,6 +14,7 @@ import (
 type UserRepository interface {
 	Create(user *model.User) error
 	GetByID(id string) (*model.User, error)
+	GetUsersByIDs(ctx context.Context, ids []string) (map[string]*model.User, error)
 	GetByUsername(username string) (*model.User, error)
 	GetByEmail(email string) (*model.User, error)
 	GetByPhone(phone string) (*model.User, error)
@@ -607,3 +609,22 @@ func (r *userRepository) GetPendingDeletionUsers(beforeTime time.Time) ([]*model
 func (r *userRepository) HardDeleteUser(userID string) error {
 	return r.db.Unscoped().Delete(&model.User{}, "id = ?", userID).Error
 }
+
+// GetUsersByIDs 批量获取用户信息
+func (r *userRepository) GetUsersByIDs(ctx context.Context, ids []string) (map[string]*model.User, error) {
+	result := make(map[string]*model.User, len(ids))
+	if len(ids) == 0 {
+		return result, nil
+	}
+
+	var users []*model.User
+	err := r.db.WithContext(ctx).Where("id IN ?", ids).Find(&users).Error
+	if err != nil {
+		return nil, err
+	}
+
+	for _, u := range users {
+		result[u.ID] = u
+	}
+	return result, nil
+}