TiCDC 同步 SQL_MODE 相关
- 2024-10-25 北京
本文字数:4363 字
阅读完需:约 14 分钟
作者: Brian 原文来源:https://tidb.net/blog/91f38d0b
问题澄清
下游 users 表中 username 列默认为非空,所以 ticdc 应该会同步报错。但是为何 ticdc 并没有同步报错,user_id = 2 同步成功,userame 的数据还和上游不一样?
问题背景
集群版本:v6.5.3
工具版本:v6.5.3
上游表结构:username 列为 default null
mysql> show create table users;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users | CREATE TABLE `users` (
`user_id` int(11) NOT NULL,
`username` varchar(50) DEFAULT NULL,
PRIMARY KEY (`user_id`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
下游表结构:username 列为 not null
mysql> show create table users;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users | CREATE TABLE `users` (
`user_id` int(11) NOT NULL,
`username` varchar(50) NOT NULL,
PRIMARY KEY (`user_id`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
上游执行语句:
mysql> insert into users (user_id ) values (2);
Query OK, 1 row affected (0.00 sec)
mysql> select * from users;
+---------+----------+
| user_id | username |
+---------+----------+
| 2 | NULL |
+---------+----------+
1 row in set (0.00 sec)
下游表数据:
mysql> select * from users;
+---------+----------+
| user_id | username |
+---------+----------+
| 2 | |
+---------+----------+
1 row in set (0.00 sec)
问题分析
1.dashboard–SQL statement
上游执行
insert into users (user_id ) values (2);
查看下游实际执行的 SQL 为:
INSERT INTO `work`.`users` (`user_id`, `username`) VALUES(2, NULL)
2.sql mode 查看
当前 SQL mode 上下游相同,均为默认 SQL MODE
mysql> show variables like 'sql_mode';
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
SQL_MODE 中包含 strict_trans_tables 按理说不应该出现这种违反约束的问题
3. 分析源码
ticdc 同步会临时改变 SQL MODE 如下代码:
会将 STRICT_TRANS_TABLES,STRICT_ALL_TABLES disable 掉。
func AdjustSQLModeCompatible(sqlModes string) (string, error) {
needDisable := []string{
"NO_ZERO_IN_DATE",
"NO_ZERO_DATE",
"ERROR_FOR_DIVISION_BY_ZERO",
"NO_AUTO_CREATE_USER",
"STRICT_TRANS_TABLES",
"STRICT_ALL_TABLES",
}
needEnable := []string{
"IGNORE_SPACE",
"NO_AUTO_VALUE_ON_ZERO",
"ALLOW_INVALID_DATES",
}
disable := strings.Join(needDisable, ",")
enable := strings.Join(needEnable, ",")
mode, err := tmysql.GetSQLMode(sqlModes)
if err != nil {
return sqlModes, err
}
disableMode, err2 := tmysql.GetSQLMode(disable)
if err2 != nil {
return sqlModes, err2
}
enableMode, err3 := tmysql.GetSQLMode(enable)
if err3 != nil {
return sqlModes, err3
}
// About this bit manipulation, details can be seen
// https://github.com/pingcap/dm/pull/1869#discussion_r669771966
mode = (mode &^ disableMode) | enableMode
return GetSQLModeStrBySQLMode(mode), nil
}
4.tidb 将严格模式禁用后
如下:
#tidb数据库中默认的SQL mode
mysql> show variables like '%sql_mode%';
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Variable_name | Value |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
| sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
#表结构中,username有约数据not null
mysql> show create table users;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users | CREATE TABLE `users` (
`user_id` int(11) NOT NULL,
`username` varchar(50) NOT NULL,
PRIMARY KEY (`user_id`) /*T![clustered_index] CLUSTERED */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
#临时手动将默认有的STRICT_TRANS_TABLES禁用
mysql> set session sql_mode ="ONLY_FULL_GROUP_BY,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION";
Query OK, 0 rows affected (0.00 sec)
#username列插入null,成功插入伴有warning
mysql> insert into users values(4,null);
Query OK, 1 row affected, 1 warning (0.00 sec)
mysql> show warnings;
+---------+------+----------------------------------+
| Level | Code | Message |
+---------+------+----------------------------------+
| Warning | 1048 | Column 'username' cannot be null |
+---------+------+----------------------------------+
1 row in set (0.00 sec)
根因总结
上下游表结构不完全不一致,上游 username 列 default null,下游 username 列 not null。
Ticdc v6.5.3 同步是会临时将 STRICT_TRANS_TABLES,STRICT_ALL_TABLES 禁用,这样即使下游表列约束为 not null,也可以成功插入 null 值,但是会伴随着对应 warning
问题后续
https://github.com/pingcap/tiflow/pull/10644/files 第一次发版是 v8.0.0
上述 PR 合并之前,首先查询下游 SQL 模式,然后进行配置。该 PR 合并之后,不再查询下游,直接基于 TiDB 的默认 SQL 模式进行配置。使用配置后的 SQL 模式创建到下游系统的连接。
备注
关于此 case 的解决在此要特别感谢产研 jinling 老师!
版权声明: 本文为 InfoQ 作者【TiDB 社区干货传送门】的原创文章。
原文链接:【http://xie.infoq.cn/article/97b281f0730851104e2db2308】。文章转载请联系作者。
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