refactor(messaging): shift sequence generation responsibility to database transactions

Move the responsibility of sequence (`seq`) allocation from the application/cache layer to the database layer to ensure absolute consistency. Previously, sequences were pre-allocated via Redis/Lua, which introduced complexity in managing synchronization between the cache and the database.

Key changes:
- Implement `CreateMessageWithSeq` in `message_repo.go` using `SELECT FOR UPDATE` to lock the conversation row and atomically increment the `last_seq` within a single transaction.
- Simplify `SeqBufferManager` by removing the complex local buffering and Lua-based pre-allocation logic, reverting to a simpler model.
- Update `chat_service.go`, `group_service.go`, and `message_service.go` to remove manual sequence retrieval, relying instead on the repository's transactional allocation.
- Introduce `SyncConvSeq` in `conversation_cache.go` to perform "write-through" updates to Redis, ensuring the cache remains synchronized with the database's source of truth.
- Improve cold-start handling in `conversation_cache.go` with a new `syncSeqLua` script to prevent stale sequence reads.

internal/cache/conversation_cache.go

@@ -9,6 +9,7 @@ import (
 	"github.com/redis/go-redis/v9"
 
 	"with_you/internal/model"
+	redisPkg "with_you/internal/pkg/redis"
 
 	"go.uber.org/zap"
 )
@@ -31,6 +32,14 @@ redis.call('SETNX', seqKey, initVal)
 return redis.call('INCR', seqKey)
 `)
 
+// syncSeqLua 写透缓存：确保 Redis seq >= DB seq，防止冷启动后读到过期值
+var syncSeqLua = redis.NewScript(`
+local current = tonumber(redis.call('GET', KEYS[1]))
+if current == nil or current < tonumber(ARGV[1]) then
+  redis.call('SET', KEYS[1], ARGV[1])
+end
+`)
+
 // CachedConversation 带缓存元数据的会话
 type CachedConversation struct {
 	Data      *model.Conversation // 实际数据
@@ -713,86 +722,58 @@ func (c *ConversationCache) ComputeAllUnreadCount(ctx context.Context, userID st
 	return total, nil
 }
 
-// GetNextSeq 获取会话的下一个 seq 值（原子递增）
-// 启用 seq 预分配时使用本地缓冲区 + Redis Lua 分配；否则使用旧 INCR 逻辑
+// GetNextSeq 获取会话的下一个 seq 值（单次 Redis INCR，原子无竞态）
 func (c *ConversationCache) GetNextSeq(ctx context.Context, convID string) (int64, error) {
-	// 优先使用 seq 预分配
+	// 优先使用 SeqBufferManager（已简化为单次 INCR）
 	if c.seqBufferMgr != nil && c.seqBufferMgr.IsEnabled() {
 		return c.seqBufferMgr.GetNextSeq(ctx, convID, false)
 	}
 
-	// 降级到旧逻辑：使用 Lua 脚本原子执行 INCR + 首次初始化对齐，避免竞态
 	seqKey := MessageSeqKey(convID)
 
-	// 尝试用 Lua 脚本原子递增（key 存在时 INCR，不存在时返回 0 触发冷启动）
+	// 尝试 Redis INCR（key 存在时递增，不存在时返回 0 触发冷启动）
 	if lc, ok := c.cache.(*LayeredCache); ok && lc.IsEnabled() {
 		rdb := lc.GetRedisClient()
 		if rdb != nil {
 			result, err := nextSeqLua.Run(ctx, rdb.GetClient(), []string{seqKey}).Int64()
 			if err == nil {
 				if result > 0 {
-					// key 已存在，INCR 成功
 					_ = c.cache.Expire(ctx, seqKey, c.settings.SeqTTL)
 					return result, nil
 				}
-				// result == 0: 冷启动，key 不存在，需从 DB 初始化
-				if c.repo != nil {
-					conv, dbErr := c.repo.GetConversationByID(convID)
-					if dbErr != nil {
-						return 0, fmt.Errorf("failed to load conversation for seq init: %w", dbErr)
+				// 冷启动：从 DB 加载 last_seq，SETNX+INCR 原子初始化
+				return c.initSeqFromDB(ctx, convID, seqKey, rdb)
 			}
-					initVal := conv.LastSeq // SETNX 使用 last_seq，INCR 返回 last_seq + 1
-					initResult, initErr := initSeqLua.Run(ctx, rdb.GetClient(), []string{seqKey}, initVal).Int64()
-					if initErr != nil {
-						// 初始化失败，降级到非原子路径
-						zap.L().Warn("initSeqLua failed, falling back", zap.Error(initErr))
-					} else {
-						_ = c.cache.Expire(ctx, seqKey, c.settings.SeqTTL)
-						return initResult, nil
-					}
-				}
-			}
-			// Lua 脚本失败，降级到非原子路径
 		}
 	}
 
-	// 非原子降级路径（Redis 不可用或 Lua 不支持）
-	newSeq, err := c.cache.Incr(ctx, seqKey)
-	if err != nil {
-		// Redis 不可用时降级到 DB
+	// Redis 不可用，降级到 DB（SELECT FOR UPDATE 保证原子性）
 	if c.msgRepo != nil {
 		if dbSeq, dbErr := c.msgRepo.GetNextSeq(convID); dbErr == nil {
-				c.cache.Set(seqKey, dbSeq, c.settings.SeqTTL)
 			return dbSeq, nil
 		}
 	}
-		return 0, fmt.Errorf("redis incr seq failed: %w", err)
-	}
-
-	// 首次调用时 Redis key 不存在，INCR 从 0 返回 1，需要从 DB 补齐
-	// 注意：此路径存在竞态窗口，优先使用上面的 Lua 原子路径
-	if newSeq == 1 && c.repo != nil {
-		conv, err := c.repo.GetConversationByID(convID)
-		if err != nil {
-			return 0, fmt.Errorf("failed to load conversation for seq init: %w", err)
-		}
-
-		if conv.LastSeq > 0 {
-			alignedSeq, err := c.cache.IncrBySeq(ctx, seqKey, conv.LastSeq)
-			if err != nil {
-				return conv.LastSeq + 1, nil // 降级返回 DB 值
-			}
-			newSeq = alignedSeq
-		}
-	}
-
-	// 每次 INCR 后刷新 TTL，防止 seq 计数器过期导致从头开始
-	_ = c.cache.Expire(ctx, seqKey, c.settings.SeqTTL)
-
-	return newSeq, nil
+	return 0, fmt.Errorf("seq allocation failed for %s: no redis or db available", convID)
 }
 
-// GetNextSeqWithGroup 获取会话的下一个 seq 值（支持群聊标识，用于 seq 预分配步长区分）
+// initSeqFromDB 冷启动：从 DB 加载 last_seq，用 SETNX+INCR 原子初始化
+func (c *ConversationCache) initSeqFromDB(ctx context.Context, convID, seqKey string, rdb *redisPkg.Client) (int64, error) {
+	if c.repo == nil {
+		return 0, fmt.Errorf("conversation repository not configured for seq init")
+	}
+	conv, dbErr := c.repo.GetConversationByID(convID)
+	if dbErr != nil {
+		return 0, fmt.Errorf("load conversation for seq init: %w", dbErr)
+	}
+	result, initErr := initSeqLua.Run(ctx, rdb.GetClient(), []string{seqKey}, conv.LastSeq).Int64()
+	if initErr != nil {
+		return 0, fmt.Errorf("initSeqLua failed: %w", initErr)
+	}
+	_ = c.cache.Expire(ctx, seqKey, c.settings.SeqTTL)
+	return result, nil
+}
+
+// GetNextSeqWithGroup 获取会话的下一个 seq 值（isGroup 参数保留兼容，简化后不区分步长）
 func (c *ConversationCache) GetNextSeqWithGroup(ctx context.Context, convID string, isGroup bool) (int64, error) {
 	if c.seqBufferMgr != nil && c.seqBufferMgr.IsEnabled() {
 		return c.seqBufferMgr.GetNextSeq(ctx, convID, isGroup)
@@ -800,6 +781,22 @@ func (c *ConversationCache) GetNextSeqWithGroup(ctx context.Context, convID stri
 	return c.GetNextSeq(ctx, convID)
 }
 
+// SyncConvSeq 写透缓存：将 DB 刚分配的 seq 同步到 Redis，确保 Redis seq >= DB seq
+func (c *ConversationCache) SyncConvSeq(ctx context.Context, convID string, seq int64) {
+	seqKey := MessageSeqKey(convID)
+
+	if lc, ok := c.cache.(*LayeredCache); ok && lc.IsEnabled() {
+		rdb := lc.GetRedisClient()
+		if rdb != nil {
+			_ = syncSeqLua.Run(ctx, rdb.GetClient(), []string{seqKey}, seq).Err()
+		}
+	}
+
+	if c.seqBufferMgr != nil && c.seqBufferMgr.rdb != nil {
+		_ = syncSeqLua.Run(ctx, c.seqBufferMgr.rdb, []string{seqKey}, seq).Err()
+	}
+}
+
 // ============================================================
 // 消息缓存方法
 // ============================================================

internal/cache/seq_buffer.go

@@ -3,7 +3,6 @@ package cache
 import (
 	"context"
 	"fmt"
-	"sync"
 	"time"
 
 	"github.com/redis/go-redis/v9"
@@ -12,139 +11,27 @@ import (
 	redisPkg "with_you/internal/pkg/redis"
 )
 
-// SeqBufferConfig seq 预分配配置
+const seqKeyTTL = 24 * time.Hour
+
+// SeqBufferConfig seq 预分配配置（保留结构以兼容配置文件，实际不再使用缓冲）
 type SeqBufferConfig struct {
 	Enabled           bool `mapstructure:"enabled"`
-	PrivateBufferSize int  `mapstructure:"private_buffer_size"` // 私聊预分配步长
-	GroupBufferSize   int  `mapstructure:"group_buffer_size"`  // 群聊预分配步长
-	LockTimeoutMs     int  `mapstructure:"lock_timeout_ms"`    // 分布式锁超时(ms)
-	MaxRetries        int  `mapstructure:"max_retries"`        // 冷启动重试次数
+	PrivateBufferSize int  `mapstructure:"private_buffer_size"`
+	GroupBufferSize   int  `mapstructure:"group_buffer_size"`
+	LockTimeoutMs     int  `mapstructure:"lock_timeout_ms"`
+	MaxRetries        int  `mapstructure:"max_retries"`
 }
 
-// localSeqBuffer 本地 seq 缓冲区
-type localSeqBuffer struct {
-	mu     sync.Mutex
-	curr   int64 // 当前已分配到的 seq
-	last   int64 // 本地缓冲区的上界
-}
-
-// SeqBufferManager seq 预分配管理器
+// SeqBufferManager seq 分配管理器（简化版：每条消息一个 Redis INCR，无本地缓冲）
 type SeqBufferManager struct {
-	rdb      *redis.Client // 原始 Redis 客户端（用于执行 Lua 脚本）
+	rdb     *redis.Client
 	config  SeqBufferConfig
 	repo    ConversationRepository
 	msgRepo MessageRepository
-	buffers  sync.Map // convID -> *localSeqBuffer
 }
 
-// mallocLua 预分配 Lua 跟踪脚本
-// KEYS[1] = seq_buf:{convID}  (Hash: CURR/LAST/LOCK/TIME)
-// KEYS[2] = msg_seq:{convID}  (String, 兼容旧 INCR key)
-// ARGV[1] = bufferSize
-// ARGV[2] = lockTimeoutMs (毫秒)
-// ARGV[3] = current timestamp (毫秒)
-//
-// 返回:
-//   status=1, startSeq, endSeq  — 成功分配
-//   status=2                    — 冷启动（key 不存在）
-//   status=0                    — 获取锁失败
-var mallocLua = redis.NewScript(`
-local bufKey   = KEYS[1]
-local seqKey   = KEYS[2]
-local bufSize  = tonumber(ARGV[1])
-local lockMs   = tonumber(ARGV[2])
-local nowMs    = tonumber(ARGV[3])
-
--- 尝试获取分布式锁
-local lockVal  = redis.call('HGET', bufKey, 'LOCK')
-if lockVal then
-  local lockTs = tonumber(lockVal)
-  if lockTs > 0 and (nowMs - lockTs) < lockMs then
-    return {0, 0, 0}
-  end
-end
-redis.call('HSET', bufKey, 'LOCK', nowMs)
-redis.call('HSET', bufKey, 'TIME', nowMs)
-
-local curr = tonumber(redis.call('HGET', bufKey, 'CURR'))
-local last = tonumber(redis.call('HGET', bufKey, 'LAST'))
-
-if curr == nil or last == nil then
-  -- 冷启动：key 不存在
-  redis.call('HDEL', bufKey, 'LOCK')
-  return {2, 0, 0}
-end
-
-if curr < last then
-  -- 本地缓冲区仍有余量，直接分配一个 seq
-  local newCurr = redis.call('HINCRBY', bufKey, 'CURR', 1)
-  redis.call('HDEL', bufKey, 'LOCK')
-  return {1, newCurr, last}
-end
-
--- 缓冲区耗尽，扩展 LAST
-local newLast = last + bufSize
-redis.call('HSET', bufKey, 'LAST', newLast)
--- 推进 CURR 防止下一个调用者获得相同的 start seq
-redis.call('HSET', bufKey, 'CURR', curr + 1)
--- 同步更新 msg_seq（兼容旧 INCR key，确保 READ 的值不回退）
-local oldSeq = tonumber(redis.call('GET', seqKey))
-if oldSeq and oldSeq > newLast then
-  newLast = oldSeq + bufSize
-  redis.call('HSET', bufKey, 'LAST', newLast)
-end
-redis.call('SET', seqKey, newLast)
-redis.call('HDEL', bufKey, 'LOCK')
-return {1, curr + 1, newLast}
-`)
-
-// initLua 冷启动初始化 Lua 跟踪脚本
-// KEYS[1] = seq_buf:{convID}
-// KEYS[2] = msg_seq:{convID}
-// ARGV[1] = startSeq (从 DB 获取的 conv.LastSeq)
-// ARGV[2] = bufferSize
-// ARGV[3] = lockTimeoutMs
-// ARGV[4] = current timestamp (毫秒)
-var initLua = redis.NewScript(`
-local bufKey   = KEYS[1]
-local seqKey   = KEYS[2]
-local startSeq = tonumber(ARGV[1])
-local bufSize  = tonumber(ARGV[2])
-local lockMs   = tonumber(ARGV[3])
-local nowMs    = tonumber(ARGV[4])
-
--- 创建 seq_buf Hash
-redis.call('HSET', bufKey, 'CURR', startSeq)
-redis.call('HSET', bufKey, 'LAST', startSeq + bufSize)
-redis.call('HSET', bufKey, 'LOCK', 0)
-redis.call('HSET', bufKey, 'TIME', nowMs)
-
--- 同步更新 msg_seq（兼容旧 INCR key）
-local oldSeq = tonumber(redis.call('GET', seqKey))
-if oldSeq and oldSeq > (startSeq + bufSize) then
-  redis.call('HSET', bufKey, 'LAST', oldSeq + bufSize)
-  redis.call('SET', seqKey, oldSeq + bufSize)
-else
-  redis.call('SET', seqKey, startSeq + bufSize)
-end
-
-return {1, startSeq + 1, startSeq + bufSize}
-`)
-
-// NewSeqBufferManager 创建 seq 预分配管理器
+// NewSeqBufferManager 创建 seq 分配管理器
 func NewSeqBufferManager(rdb *redis.Client, cfg SeqBufferConfig, repo ConversationRepository, msgRepo MessageRepository) *SeqBufferManager {
-	if cfg.PrivateBufferSize <= 0 {
-		cfg.PrivateBufferSize = 50
-	}
-	if cfg.GroupBufferSize <= 0 {
-		cfg.GroupBufferSize = 200
-	}
-	if cfg.LockTimeoutMs <= 0 {
-		cfg.LockTimeoutMs = 5000
-	}
-	if cfg.MaxRetries <= 0 {
-		cfg.MaxRetries = 3
-	}
 	return &SeqBufferManager{
 		rdb:     rdb,
 		config:  cfg,
@@ -153,160 +40,67 @@ func NewSeqBufferManager(rdb *redis.Client, cfg SeqBufferConfig, repo Conversati
 	}
 }
 
-// GetNextSeq 获取下一个 seq（从本地缓冲区分配，耗尽时向 Redis 预分配新区间）
-func (m *SeqBufferManager) GetNextSeq(ctx context.Context, convID string, isGroup bool) (int64, error) {
-	bufSize := m.config.PrivateBufferSize
-	if isGroup {
-		bufSize = m.config.GroupBufferSize
-	}
-
-	// 1. 检查本地缓冲区
-	bufVal, ok := m.buffers.Load(convID)
-	if ok {
-		buf := bufVal.(*localSeqBuffer)
-		buf.mu.Lock()
-		if buf.curr < buf.last {
-			seq := buf.curr + 1
-			buf.curr = seq
-			buf.mu.Unlock()
-			return seq, nil
-		}
-		buf.mu.Unlock()
-	}
-
-	// 2. 本地缓冲区耗尽或不存在，向 Redis 预分配
-	startSeq, endSeq, err := m.allocateFromRedis(ctx, convID, bufSize)
-	if err != nil {
-		return 0, fmt.Errorf("allocate from redis: %w", err)
-	}
-
-	// 3. 更新本地缓冲区（CAS 防止并发分配时丢失区间）
-	newBuf := &localSeqBuffer{curr: startSeq, last: endSeq}
-	for {
-		existing, loaded := m.buffers.LoadOrStore(convID, newBuf)
-		if !loaded {
-			// 首次插入，直接使用
-			return startSeq, nil
-		}
-		// 已有缓冲区，检查是否被其他 goroutine 刷新
-		oldBuf := existing.(*localSeqBuffer)
-		oldBuf.mu.Lock()
-		if oldBuf.curr < oldBuf.last {
-			// 旧缓冲区仍有余量，直接使用（丢弃本次分配，避免区间泄漏）
-			seq := oldBuf.curr + 1
-			oldBuf.curr = seq
-			oldBuf.mu.Unlock()
-			return seq, nil
-		}
-		// 旧缓冲区耗尽，替换为新分配的区间
-		m.buffers.Store(convID, newBuf)
-		oldBuf.mu.Unlock()
-		return startSeq, nil
-	}
-}
-
-// allocateFromRedis 向 Redis 预分配 seq 区间
-func (m *SeqBufferManager) allocateFromRedis(ctx context.Context, convID string, bufferSize int) (startSeq, endSeq int64, err error) {
-	bufKey := SeqBufferKey(convID)
+// GetNextSeq 获取下一个 seq（单次 Redis INCR，原子且无竞态）
+func (m *SeqBufferManager) GetNextSeq(ctx context.Context, convID string, _ bool) (int64, error) {
 	seqKey := MessageSeqKey(convID)
-	nowMs := time.Now().UnixMilli()
 
-	for i := 0; i < m.config.MaxRetries; i++ {
-		result, err := mallocLua.Run(ctx, m.rdb, []string{bufKey, seqKey}, bufferSize, m.config.LockTimeoutMs, nowMs).Int64Slice()
-		if err != nil {
+	// 1. 尝试 INCR（key 存在时直接递增，原子操作）
+	result, err := nextSeqLua.Run(ctx, m.rdb, []string{seqKey}).Int64()
+	if err == nil {
+		if result > 0 {
+			m.rdb.Expire(ctx, seqKey, seqKeyTTL)
+			return result, nil
+		}
+		// result == 0: 冷启动，需从 DB 初始化
+		return m.initAndIncr(ctx, convID, seqKey)
+	}
+
 	// Redis 不可用，降级到 DB
-			zap.L().Warn("seq malloc lua failed, falling back to DB", zap.String("convID", convID), zap.Error(err))
+	zap.L().Warn("seq INCR failed, falling back to DB", zap.String("convID", convID), zap.Error(err))
 	if m.msgRepo != nil {
 		if dbSeq, dbErr := m.msgRepo.GetNextSeq(convID); dbErr == nil {
-					return dbSeq, dbSeq, nil
+			return dbSeq, nil
 		}
 	}
-			return 0, 0, fmt.Errorf("lua script error: %w", err)
-		}
-
-		status := result[0]
-		switch status {
-		case 1:
-			// 成功分配
-			return result[1], result[2], nil
-		case 2:
-			// 冷启动，需要从 DB 初始化
-			startSeq, endSeq, initErr := m.initFromDB(ctx, convID, bufferSize)
-			if initErr != nil {
-				return 0, 0, fmt.Errorf("init from db: %w", initErr)
-			}
-			return startSeq, endSeq, nil
-		case 0:
-			// 获取锁失败，短暂等待后重试
-			time.Sleep(time.Duration(50) * time.Millisecond)
-			continue
-		}
-	}
-
-	// 所有重试失败，降级到 DB
-	zap.L().Warn("seq malloc retries exhausted, falling back to DB", zap.String("convID", convID))
-	if m.msgRepo != nil {
-		if dbSeq, dbErr := m.msgRepo.GetNextSeq(convID); dbErr == nil {
-			return dbSeq, dbSeq, nil
-		}
-	}
-	return 0, 0, fmt.Errorf("malloc retries exhausted")
+	return 0, fmt.Errorf("seq allocation failed for %s: %w", convID, err)
 }
 
-// initFromDB 冷启动时从 DB 加载 LastSeq 并初始化 Redis seq_buf Hash
-func (m *SeqBufferManager) initFromDB(ctx context.Context, convID string, bufferSize int) (startSeq, endSeq int64, err error) {
+// initAndIncr 冷启动：从 DB 加载 last_seq，然后用 SETNX+INCR 原子初始化
+func (m *SeqBufferManager) initAndIncr(ctx context.Context, convID, seqKey string) (int64, error) {
 	if m.repo == nil {
-		return 0, 0, fmt.Errorf("conversation repository not configured")
+		return 0, fmt.Errorf("conversation repository not configured for seq init")
 	}
 
 	conv, err := m.repo.GetConversationByID(convID)
 	if err != nil {
-		return 0, 0, fmt.Errorf("load conversation: %w", err)
+		return 0, fmt.Errorf("load conversation for seq init: %w", err)
 	}
 
-	dbLastSeq := conv.LastSeq
-	if dbLastSeq <= 0 {
-		dbLastSeq = 0
-	}
-
-	bufKey := SeqBufferKey(convID)
-	seqKey := MessageSeqKey(convID)
-	nowMs := time.Now().UnixMilli()
-
-	result, err := initLua.Run(ctx, m.rdb, []string{bufKey, seqKey}, dbLastSeq, bufferSize, m.config.LockTimeoutMs, nowMs).Int64Slice()
+	initVal := conv.LastSeq
+	result, err := initSeqLua.Run(ctx, m.rdb, []string{seqKey}, initVal).Int64()
 	if err != nil {
-		return 0, 0, fmt.Errorf("init lua script error: %w", err)
+		return 0, fmt.Errorf("initSeqLua failed: %w", err)
 	}
 
-	zap.L().Info("seq buffer cold-start initialized",
-		zap.String("convID", convID),
-		zap.Int64("dbLastSeq", dbLastSeq),
-		zap.Int64("startSeq", result[1]),
-		zap.Int64("endSeq", result[2]),
-	)
-
-	return result[1], result[2], nil
+	m.rdb.Expire(ctx, seqKey, seqKeyTTL)
+	return result, nil
 }
 
-// InvalidateBuffer 清除本地缓冲区（会话 seq 被外部重置时调用）
-func (m *SeqBufferManager) InvalidateBuffer(convID string) {
-	m.buffers.Delete(convID)
-}
+// InvalidateBuffer no-op（保留接口兼容）
+func (m *SeqBufferManager) InvalidateBuffer(convID string) {}
 
-// IsEnabled 是否启用预分配
+// IsEnabled 是否启用
 func (m *SeqBufferManager) IsEnabled() bool {
 	return m.config.Enabled && m.rdb != nil
 }
 
 // NewSeqBufferManagerFromCache 从 ConversationCache 的 Cache 接口创建 SeqBufferManager
-// 当 wire 中不方便注入 redis.Client 时，可通过 Cache 接口获取底层 Redis 连接
 func NewSeqBufferManagerFromCache(cacheBackend Cache, cfg SeqBufferConfig, repo ConversationRepository, msgRepo MessageRepository) *SeqBufferManager {
 	redisCache, ok := cacheBackend.(*RedisCache)
 	if !ok {
 		zap.L().Warn("SeqBuffer: cache is not RedisCache, seq pre-allocation disabled")
 		return &SeqBufferManager{config: cfg, repo: repo, msgRepo: msgRepo}
 	}
-
 	rdb := redisCache.GetRedisClient().GetClient()
 	return NewSeqBufferManager(rdb, cfg, repo, msgRepo)
 }

internal/repository/message_repo.go

@@ -431,40 +431,43 @@ func (r *messageRepository) GetNextSeq(conversationID string) (int64, error) {
 	return nextSeq, err
 }
 
-// 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
+// CreateMessageWithSeq 创建消息并在事务内原子分配 seq
+// DB 是 seq 的唯一真相来源：SELECT FOR UPDATE 锁行 → last_seq+1 → 写入消息 → 更新 last_seq
+// msg.Seq 会在事务内被设置，调用方无需预先分配
 func (r *messageRepository) CreateMessageWithSeq(msg *model.Message) error {
 	return r.db.Transaction(func(tx *gorm.DB) error {
-		// 创建消息（seq 已由调用方预分配）
+		// 1. 锁定会话行，读取当前 last_seq
+		var conv model.Conversation
+		query := tx.Where("id = ?", msg.ConversationID)
+		if tx.Dialector.Name() == "postgres" {
+			query = query.Clauses(clause.Locking{Strength: "UPDATE"})
+		}
+		if err := query.First(&conv).Error; err != nil {
+			return fmt.Errorf("lock conversation for seq: %w", err)
+		}
+
+		// 2. 原子分配 seq
+		msg.Seq = conv.LastSeq + 1
+
+		// 3. 创建消息
 		if err := tx.Create(msg).Error; err != nil {
 			return err
 		}
 
-		// 更新会话last_seq：仅当新 seq 更大时才更新，防止并发写入导致 last_seq 回退
-		result := tx.Model(&model.Conversation{}).
-			Where("id = ? AND last_seq < ?", msg.ConversationID, msg.Seq).
+		// 4. 更新会话 last_seq 和 last_msg_time
+		if err := tx.Model(&model.Conversation{}).
+			Where("id = ?", msg.ConversationID).
 			Updates(map[string]any{
 				"last_seq":      msg.Seq,
 				"last_msg_time": gorm.Expr("CURRENT_TIMESTAMP"),
-			})
-		if result.Error != nil {
-			return result.Error
-		}
-		// 当 last_seq >= msg.Seq 时（并发写入已更新），仍需刷新 last_msg_time
-		if err := tx.Model(&model.Conversation{}).
-			Where("id = ? AND last_seq >= ?", msg.ConversationID, msg.Seq).
-			Update("last_msg_time", gorm.Expr("CURRENT_TIMESTAMP")).Error; err != nil {
+			}).Error; err != nil {
 			return err
 		}
 
-		// 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{}).
+		// 5. 新消息到达后，自动恢复被"仅自己删除"的会话
+		return tx.Model(&model.ConversationParticipant{}).
 			Where("conversation_id = ?", msg.ConversationID).
-			Update("hidden_at", nil).Error; err != nil {
-			return err
-		}
-
-		return nil
+			Update("hidden_at", nil).Error
 	})
 }
 

internal/service/chat_service.go

@@ -479,20 +479,18 @@ 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.GetNextSeqWithGroup(ctx, conversationID, conv.Type == model.ConversationTypeGroup)
-		if err != nil {
-			return nil, fmt.Errorf("failed to get next seq for conversation %s: %w", conversationID, err)
-		}
-		message.Seq = seq
-	}
+		// seq 由 CreateMessageWithSeq 在事务内原子分配
 
 	// 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)
 	}
 
+	// 写透 seq 到 Redis，保持缓存与 DB 一致
+	if s.conversationCache != nil {
+		s.conversationCache.SyncConvSeq(context.Background(), conversationID, message.Seq)
+	}
+
 	// 发送者自动已读：将发送者的 lastReadSeq 更新到消息 seq
 	_ = s.repo.UpdateLastReadSeq(conversationID, senderID, message.Seq)
 	if s.conversationCache != nil {
@@ -1042,7 +1040,7 @@ func (s *chatServiceImpl) IsUserOnline(userID string) bool {
 // 适用于群聊等由调用方自行负责推送的场景
 func (s *chatServiceImpl) SaveMessage(ctx context.Context, senderID string, conversationID string, segments model.MessageSegments, replyToID *string) (*model.Message, error) {
 	// 验证会话是否存在
-	conv, err := s.getConversation(ctx, conversationID)
+	_, err := s.getConversation(ctx, conversationID)
 	if err != nil {
 		if errors.Is(err, gorm.ErrRecordNotFound) {
 			return nil, errors.New("会话不存在，请重新创建会话")
@@ -1073,19 +1071,17 @@ 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.GetNextSeqWithGroup(ctx, conversationID, conv.Type == model.ConversationTypeGroup)
-		if err != nil {
-			return nil, fmt.Errorf("failed to get next seq for conversation %s: %w", conversationID, err)
-		}
-		message.Seq = seq
-	}
+		// seq 由 CreateMessageWithSeq 在事务内原子分配
 
 	if err := s.repo.CreateMessageWithSeq(message); err != nil {
 		return nil, fmt.Errorf("failed to save message: %w", err)
 	}
 
+	// 写透 seq 到 Redis，保持缓存与 DB 一致
+	if s.conversationCache != nil {
+		s.conversationCache.SyncConvSeq(context.Background(), conversationID, message.Seq)
+	}
+
 	// 新消息会改变分页结果，先失效分页缓存，避免读到旧列表
 	if s.conversationCache != nil {
 		s.conversationCache.InvalidateMessagePages(conversationID)

internal/service/group_service.go

@@ -471,18 +471,7 @@ func (s *groupService) broadcastMemberJoinNotice(groupID string, targetUserID st
 				Status:   model.MessageStatusNormal,
 				Category: model.CategoryNotification,
 			}
-			// 从 Redis 获取下一个 seq
-			if s.conversationCache != nil {
-				seq, seqErr := s.conversationCache.GetNextSeqWithGroup(context.Background(), conv.ID, true)
-				if seqErr != nil {
-					zap.L().Warn("get next seq failed, skipping system message",
-						zap.String("convID", conv.ID),
-						zap.Error(seqErr),
-					)
-					return
-				}
-				msg.Seq = seq
-			}
+			// seq 由 CreateMessageWithSeq 在事务内原子分配
 			if err := s.messageRepo.CreateMessageWithSeq(msg); err != nil {
 				zap.L().Warn("保存入群提示消息失败",
 					zap.String("component", "broadcastMemberJoinNotice"),
@@ -492,6 +481,9 @@ func (s *groupService) broadcastMemberJoinNotice(groupID string, targetUserID st
 				)
 			} else {
 				savedMessage = msg
+				if s.conversationCache != nil {
+					s.conversationCache.SyncConvSeq(context.Background(), conv.ID, msg.Seq)
+				}
 				s.invalidateConversationCachesAfterSystemMessage(conv.ID)
 			}
 		} else {
@@ -1396,18 +1388,7 @@ func (s *groupService) MuteMember(userID string, groupID string, targetUserID st
 				Category: model.CategoryNotification,
 			}
 
-			// 从 Redis 获取下一个 seq
-			if s.conversationCache != nil {
-				seq, seqErr := s.conversationCache.GetNextSeqWithGroup(context.Background(), conv.ID, true)
-				if seqErr != nil {
-					zap.L().Warn("get next seq failed, skipping system message",
-						zap.String("convID", conv.ID),
-						zap.Error(seqErr),
-					)
-					return nil
-				}
-				msg.Seq = seq
-			}
+			// seq 由 CreateMessageWithSeq 在事务内原子分配
 
 			if err := s.messageRepo.CreateMessageWithSeq(msg); err != nil {
 				zap.L().Warn("保存禁言消息失败",
@@ -1421,6 +1402,9 @@ func (s *groupService) MuteMember(userID string, groupID string, targetUserID st
 					zap.String("msgID", msg.ID),
 					zap.Int64("seq", msg.Seq),
 				)
+				if s.conversationCache != nil {
+					s.conversationCache.SyncConvSeq(context.Background(), conv.ID, msg.Seq)
+				}
 				s.invalidateConversationCachesAfterSystemMessage(conv.ID)
 			}
 		} else {

internal/service/message_service.go

@@ -2,7 +2,6 @@ package service
 
 import (
 	"context"
-	"fmt"
 	"time"
 
 	"with_you/internal/cache"
@@ -88,21 +87,17 @@ func (s *MessageService) SendMessage(ctx context.Context, senderID, receiverID s
 		Status:         model.MessageStatusNormal,
 	}
 
-	// 从 Redis 获取下一个 seq
-	if s.conversationCache != nil {
-		seq, seqErr := s.conversationCache.GetNextSeqWithGroup(context.Background(), conv.ID, false)
-		if seqErr != nil {
-			return nil, fmt.Errorf("failed to get next seq for conversation %s: %w", conv.ID, seqErr)
-		}
-		msg.Seq = seq
-	}
-
-	// 使用事务创建消息并更新seq
+	// 事务内原子分配 seq + 创建消息（DB 是 seq 唯一来源）
 	err = s.messageRepo.CreateMessageWithSeq(msg)
 	if err != nil {
 		return nil, err
 	}
 
+	// 写透 seq 到 Redis，保持缓存与 DB 一致
+	if s.conversationCache != nil {
+		s.conversationCache.SyncConvSeq(context.Background(), conv.ID, msg.Seq)
+	}
+
 	// 新消息会改变分页结果，先失效分页缓存，避免读到旧列表
 	if s.conversationCache != nil {
 		s.conversationCache.InvalidateMessagePages(conv.ID)