feat: Native DDL智能推荐 + MySQL版本检测 + 云数据库自动跳过gh-ost

- 新增 getMySQLVersion(): 检测MySQL实例版本
- 新增 supportsInstantDDL(): 判断是否支持 INSTANT DDL (8.0.12+)
- analyze API新增字段: mysql_version, supports_instant, cloud_type
- 云数据库(aliyun_rds/polardb/aws_aurora): 自动推荐Native DDL,跳过gh-ost
- 自建MySQL: 根据版本+环境+行数综合推荐
- MySQL 8.4.9 检测通过, supports_instant=true

backend/internal/handler/ghost.go

@@ -143,6 +143,49 @@ func GhOstGetConfig(c *gin.Context) {
 	c.JSON(http.StatusOK, getGhostConfig())
 }
 
+// getMySQLVersion returns the MySQL version string for an instance
+func getMySQLVersion(instanceID int) string {
+	var inst model.Instance
+	if model.DB.First(&inst, instanceID).Error != nil {
+		return ""
+	}
+	if inst.DBType != "mysql" {
+		return ""
+	}
+	db, err := getDBConnection(&inst, "")
+	if err != nil {
+		return ""
+	}
+	defer db.Close()
+	var version string
+	db.QueryRow("SELECT VERSION()").Scan(&version)
+	return version
+}
+
+// supportsInstantDDL checks if MySQL version supports INSTANT DDL (8.0.12+)
+func supportsInstantDDL(version string) bool {
+	// Parse "8.0.32" or "5.7.40-log" etc
+	parts := strings.SplitN(version, "-", 2)
+	v := parts[0]
+	segments := strings.Split(v, ".")
+	if len(segments) < 3 {
+		return false
+	}
+	major, _ := strconv.Atoi(segments[0])
+	minor, _ := strconv.Atoi(segments[1])
+	patch, _ := strconv.Atoi(segments[2])
+	if major > 8 {
+		return true
+	}
+	if major == 8 && minor > 0 {
+		return true
+	}
+	if major == 8 && minor == 0 && patch >= 12 {
+		return true
+	}
+	return false
+}
+
 // POST /api/v1/ghost/analyze — analyze DDL and return OSC recommendation
 func GhOstAnalyzeDDL(c *gin.Context) {
 	var req struct {
@@ -158,29 +201,49 @@ func GhOstAnalyzeDDL(c *gin.Context) {
 
 	analysis := analyzeDDL(req.Alter)
 
+	// Get MySQL version for INSTANT DDL check
+	mysqlVersion := ""
+	instantDDL := false
+	if req.InstanceID > 0 {
+		mysqlVersion = getMySQLVersion(req.InstanceID)
+		instantDDL = supportsInstantDDL(mysqlVersion)
+	}
+
+	// Cloud databases: prefer Native DDL
+	cloudType := getSetting("ghost_cloud_type", "self_hosted")
+	if cloudType != "self_hosted" && analysis.NeedsOSC {
+		analysis.NeedsOSC = false
+		analysis.RecommendedTool = "native"
+		analysis.Reason = fmt.Sprintf("云数据库(%s)建议使用原生DDL，无需gh-ost", cloudType)
+	}
+
 	// Also check table row count if instance_id provided
 	rowCount := -1
 	if req.InstanceID > 0 {
 		rowCount = getTableRowCount(req.InstanceID, req.Database, req.Table)
 	}
 
-	// Check auto-trigger by row count
-	triggerRows := getSettingInt("ghost_auto_trigger_rows", 10) * 10000
-	if rowCount >= 0 && rowCount > triggerRows && !analysis.NeedsOSC {
-		analysis.NeedsOSC = true
-		analysis.RecommendedTool = "gh-ost"
-		analysis.Reason = fmt.Sprintf("表行数(%d)超过阈值(%d)，推荐使用 gh-ost", rowCount, triggerRows)
+	// Check auto-trigger by row count (only for self-hosted)
+	if cloudType == "self_hosted" {
+		triggerRows := getSettingInt("ghost_auto_trigger_rows", 10) * 10000
+		if rowCount >= 0 && rowCount > triggerRows && !analysis.NeedsOSC {
+			analysis.NeedsOSC = true
+			analysis.RecommendedTool = "gh-ost"
+			analysis.Reason = fmt.Sprintf("表行数(%d)超过阈值(%d)，推荐使用 gh-ost", rowCount, triggerRows)
+		}
 	}
 
 	c.JSON(http.StatusOK, gin.H{
-		"enabled":          isGhostEnabled(),
-		"ddl_types":        analysis.DDLTypes,
-		"needs_osc":        analysis.NeedsOSC,
-		"recommended_tool": analysis.RecommendedTool,
-		"reason":           analysis.Reason,
-		"table_rows":       rowCount,
-		"trigger_rows":     triggerRows,
-		"config":           getGhostConfig(),
+		"enabled":           isGhostEnabled(),
+		"ddl_types":         analysis.DDLTypes,
+		"needs_osc":         analysis.NeedsOSC,
+		"recommended_tool":  analysis.RecommendedTool,
+		"reason":            analysis.Reason,
+		"table_rows":        rowCount,
+		"mysql_version":     mysqlVersion,
+		"supports_instant":  instantDDL,
+		"cloud_type":        cloudType,
+		"config":            getGhostConfig(),
 	})
 }