基於statement或mixed格式的主從複製真的安全嗎?
阿新 • • 發佈:2022-05-28
作為支援工程師,我仍然可以看到不少客戶使用STATEMENT或MIXED格式,即使他們已經使用 MySQL 8.0。在許多情況下這沒問題,但最近我不得不處理一個非常討厭的情況,發現不使用ROW格式會導致副本默默地丟失資料更新,而不會引發任何複製錯誤! 這是一些非常罕見的邊緣用例嗎? 一點也不! 讓我在下面演示一個非常簡單的測試用例,以說明最終陷入如此糟糕的情況是多麼容易。
測試一
主庫
mysql> select @@binlog_format,@@system_time_zone; +-----------------+--------------------+ | @@binlog_format | @@system_time_zone | +-----------------+--------------------+ | STATEMENT | BST | +-----------------+--------------------+ 1 row in set (0.00 sec) mysql> CREATE TABLE `test1` ( -> `id` int(11) NOT NULL AUTO_INCREMENT, -> `d` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, -> `a` varchar(30) NOT NULL, -> `name` varchar(25) DEFAULT NULL, -> PRIMARY KEY (`a`), -> UNIQUE KEY `id` (`id`) -> ) ENGINE=InnoDB; Query OK, 0 rows affected, 1 warning (0.02 sec) mysql> insert into test1 values (null,now(),"test1",0); Query OK, 1 row affected (0.00 sec) mysql> insert into test1 values (null,now(),"test2",0); Query OK, 1 row affected (0.01 sec) mysql> insert into test1 values (null,now(),"test3",0); Query OK, 1 row affected (0.01 sec) mysql> select * from test1; +----+---------------------+-------+------+ | id | d | a | name | +----+---------------------+-------+------+ | 1 | 2022-05-22 10:13:37 | test1 | 0 | | 2 | 2022-05-22 10:13:37 | test2 | 0 | | 3 | 2022-05-22 10:13:38 | test3 | 0 | +----+---------------------+-------+------+ 3 rows in set (0.00 sec)
從庫
mysql> select @@system_time_zone; +--------------------+ | @@system_time_zone | +--------------------+ | UTC | +--------------------+ 1 row in set (0.00 sec) mysql> select * from db1.test1; +----+---------------------+-------+------+ | id | d | a | name | +----+---------------------+-------+------+ | 1 | 2022-05-22 09:13:37 | test1 | 0 | | 2 | 2022-05-22 09:13:37 | test2 | 0 | | 3 | 2022-05-22 09:13:38 | test3 | 0 | +----+---------------------+-------+------+ 3 rows in set (0.00 sec)
主庫update
mysql> UPDATE test1 SET name = 'foobar', d = CURRENT_TIMESTAMP WHERE a = 'test1' AND d = '2022-05-22 10:13:37'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from test1; +----+---------------------+-------+--------+ | id | d | a | name | +----+---------------------+-------+--------+ | 1 | 2022-05-22 10:16:15 | test1 | foobar | | 2 | 2022-05-22 10:13:37 | test2 | 0 | | 3 | 2022-05-22 10:13:38 | test3 | 0 | +----+---------------------+-------+--------+ 3 rows in set (0.00 sec)
從庫檢視
mysql> select * from db1.test1; +----+---------------------+-------+------+ | id | d | a | name | +----+---------------------+-------+------+ | 1 | 2022-05-22 09:13:37 | test1 | 0 | | 2 | 2022-05-22 09:13:37 | test2 | 0 | | 3 | 2022-05-22 09:13:38 | test3 | 0 | +----+---------------------+-------+------+ 3 rows in set (0.00 sec) mysql> pager egrep "Running|SQL_Error" PAGER set to 'egrep "Running|SQL_Error"' mysql > show replica status\G Replica_IO_Running: Yes Replica_SQL_Running: Yes Last_SQL_Error: Replica_SQL_Running_State: Replica has read all relay log; waiting for more updates Last_SQL_Error_Timestamp: 1 row in set (0.00 sec)
測試二
另一個測試,使用UTC_TIME()函式
主庫
mysql> select * from test1 WHERE TIME(d) > DATE_SUB(UTC_TIME(), INTERVAL 11 HOUR) AND id=3; +----+---------------------+-------+------+ | id | d | a | name | +----+---------------------+-------+------+ | 3 | 2022-05-22 10:13:38 | test3 | 0 | +----+---------------------+-------+------+ 1 row in set (0.00 sec)
從庫
mysql> select * from test1 WHERE TIME(d) > DATE_SUB(UTC_TIME(), INTERVAL 11 HOUR) AND id=3; Empty set (0.00 sec)
測試三
主庫
mysql> update test1 set name="bar" WHERE TIME(d) > DATE_SUB(UTC_TIME(), INTERVAL 11 HOUR) AND id=3; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from test1 where id=3; +----+---------------------+-------+------+ | id | d | a | name | +----+---------------------+-------+------+ | 3 | 2022-05-22 22:12:15 | test3 | bar | +----+---------------------+-------+------+ 1 row in set (0.01 sec)
從庫
mysql> select * from test1 where id=3; +----+---------------------+-------+------+ | id | d | a | name | +----+---------------------+-------+------+ | 3 | 2022-05-22 09:13:38 | test3 | 0 | +----+---------------------+-------+------+ 1 row in set (0.01 sec) mysql > show replica status\G Replica_IO_Running: Yes Replica_SQL_Running: Yes Last_SQL_Error: Replica_SQL_Running_State: Replica has read all relay log; waiting for more updates Last_SQL_Error_Timestamp: 1 row in set (0.00 sec)
複製忽略了update,且沒有報任何複製錯誤。預計這種特殊情況會在地理分佈的資料庫環境中經常發生。
因為這些函式對主從複製是不安全的,兩個安全操作沒有被執行:
·當使用statement格式的時候,在錯誤日誌中沒有列印警告資訊
·使用mixed格式的時候,複製事件不是以RBR格式記錄的,而是使用和查詢一樣的格式
這個問題很危險,具體可以看bug提交:https://bugs.mysql.com/bug.php?id=107293
總結
基於ROW的複製已經成為MySQL中的標準並且是最可靠的一種。它也是唯一一種允許虛擬同步複製解決方案(如 Percona XtraDB Cluster/Galera 和 MySQL Group Replication)的解決方案。
同時,STATEMENT甚至MIXED格式都可能導致資料一致性問題,可能會長時間未被檢測到,從而導致最終發生複製錯誤時很難調查。
最好早點切換成row格式。