MySQL 5.6 vs 5.7 Undo 回滾段分配差異詳解

MySQL 5.6 vs 5.7 Undo 回滾段分配差異詳解

MySQL 5.7 引入獨立臨時表空間，導致 Undo Log 分配邏輯發生變化。

核心差異

官方文檔原文

As of MySQL 5.7.2, 32 undo logs are reserved for use by temporary tables and are hosted in the temporary table tablespace (ibtmp1). To allocate additional undo logs for data-modifying transactions... innodb_undo_logs must be set to a value greater than 32 if undo logs are stored in the system tablespace only. If you have configured separate undo tablespaces, innodb_undo_logs must be set to a value greater than 33...

實踐建議

• 5.7+ 使用獨立 undo 表空間（innodb_undo_tablespaces），便於管理與磁盤隔離
• 監控 SHOW ENGINE INNODB STATUS 中 History list length，防止長事務導致 undo 膨脹
• 每個 undo segment 最多支援 1024 並發事務