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移除书签使用 TiDB Data Migration 处理出错的 DDL 语句
本文介绍了如何使用 TiDB Data Migration (DM) 来处理出错的 DDL 语句。
目前，TiDB 并不完全兼容所有的 MySQL 语法（详见 DDL 的限制）。当使用 DM 从 MySQL 迁移数据到 TiDB 时，如果 TiDB 不支持对应的 DDL 语句，可能会造成错误并中断迁移任务。在这种情况下，DM 提供 binlog 命令来恢复迁移。
使用限制
如果业务不能接受下游 TiDB 跳过异常的 DDL 语句，也不接受使用其他 DDL 语句作为替代，不接受插入其他 DDL 语句，则不适合使用此方式进行处理。
比如：DROP PRIMARY KEY，这种情况下，只能在下游重建一个（DDL 执行完后的）新表结构对应的表，并将原表的全部数据重新导入该新表。
支持场景
迁移过程中，上游执行了 TiDB 不支持的 DDL 语句并迁移到了 DM，造成迁移任务中断。
- 如果业务能接受下游 TiDB 不执行该 DDL 语句，则使用
binlog skip <task-name>跳过对该 DDL 语句的迁移以恢复迁移任务。 - 如果业务能接受下游 TiDB 执行其他 DDL 语句来作为替代，则使用
binlog replace <task-name>替代该 DDL 的迁移以恢复迁移任务。 - 如果业务能接受下游 TiDB 插入执行其他 DDL 语句，则使用
binlog inject <task-name>插入其他 DDL 以恢复迁移任务。
命令介绍
使用 dmctl 手动处理出错的 DDL 语句时，主要使用的命令包括 query-status、binlog。
query-status
query-status 命令用于查询当前 MySQL 实例内子任务及 relay 单元等的状态和错误信息，详见查询状态。
binlog
binlog 命令管理和查看 binlog 操作。命令仅在 DM v6.0 及其以后版本支持，之前版本可使用 handle-error 命令。
binlog 命令用法如下：
binlog -h
manage or show binlog operationsUsage:dmctl binlog [command]Available Commands:inject inject the current error event or a specific binlog position (binlog-pos) with some ddlslist list error handle command at binlog position (binlog-pos) or after binlog position (binlog-pos)replace replace the current error event or a specific binlog position (binlog-pos) with some ddlsrevert revert the current binlog operation or a specific binlog position (binlog-pos) operationskip skip the current error event or a specific binlog position (binlog-pos) eventFlags:-b, --binlog-pos string position used to match binlog event if matched the binlog operation will be applied. The format like "mysql-bin|000001.000003:3270"-h, --help help for binlogGlobal Flags:-s, --source strings MySQL Source ID.Use "dmctl binlog [command] --help" for more information about a command.
binlog 支持如下子命令：
inject：在 DDL binlog 位置插入 DDL 语句，binlog 位置指定方式参考-b, --binlog-pos。list：查看 binlog 位置以及此位置之后的有效 inject/skip/replace 操作，binlog 位置指定方式参考-b, --binlog-pos。replace：替代 DDL binlog 位置的 DDL 语句，binlog 位置指定方式参考-b, --binlog-pos。revert：重置 binlog 位置的 inject/skip/replace 操作，仅在先前的操作没有最终生效前执行，binlog 位置指定方式参考-b, --binlog-posskip：跳过 binlog 位置的 DDL 语句, binlog 位置指定方式参考-b, --binlog-pos。
binlog 支持如下参数：
-b, --binlog-pos：- 类型：string。
- 指定 binlog 位置，表示操作将在
binlog-pos与 binlog event 的 position 匹配时生效。若不指定，DM 会默认置为当前出错的 DDL 语句的 binlog 位置。 - 格式：
binlog-filename:binlog-pos，例如mysql-bin|000001.000003:3270。 - 在迁移执行出错后，binlog position 可直接从
query-status返回的startLocation中的position获得；在迁移执行出错前，binlog position 可在上游 MySQL 中使用 SHOW BINLOG EVENTS 获得。
-s, --source strings：- 类型：string。
source指定预设操作将生效的 MySQL 实例。
- 其他参数参考
-h提示。
使用示例
迁移中断执行跳过操作
如需在迁移中断时执行跳过操作，可使用 binlog skip 命令：
binlog skip -h
skip the current error event or a specific binlog position (binlog-pos) eventUsage:dmctl binlog skip <task-name> [flags]Flags:-h, --help help for skipGlobal Flags:-b, --binlog-pos string position used to match binlog event if matched the binlog operation will be applied. The format like "mysql-bin|000001.000003:3270"-s, --source strings MySQL Source ID.
非合库合表场景
假设现在需要将上游的 db1.tbl1 表迁移到下游 TiDB，初始时表结构为：
SHOW CREATE TABLE db1.tbl1;
+-------+--------------------------------------------------+| Table | Create Table |+-------+--------------------------------------------------+| tbl1 | CREATE TABLE `tbl1` (`c1` int(11) NOT NULL,`c2` decimal(11,3) DEFAULT NULL,PRIMARY KEY (`c1`)) ENGINE=InnoDB DEFAULT CHARSET=latin1 |+-------+--------------------------------------------------+
此时，上游执行以下 DDL 操作修改表结构（将列的 DECIMAL(11, 3) 修改为 DECIMAL(10, 3)）：
ALTER TABLE db1.tbl1 CHANGE c2 c2 DECIMAL (10, 3);
则会由于 TiDB 不支持该 DDL 语句而导致 DM 迁移任务中断，使用 query-status <task-name> 命令可看到如下错误：
ERROR 8200 (HY000): Unsupported modify column: can't change decimal column precision
假设业务上可以接受下游 TiDB 不执行此 DDL 语句（即继续保持原有的表结构），则可以通过使用 binlog skip <task-name> 命令跳过该 DDL 语句以恢复迁移任务。操作步骤如下：
使用
binlog skip <task-name>跳过当前错误的 DDL 语句» binlog skip test
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-01","worker": "worker1"}]}
使用
query-status <task-name>查看任务状态» query-status test
执行结果
{"result": true,"msg": "","sources": [{"result": true,"msg": "","sourceStatus": {"source": "mysql-replica-01","worker": "worker1","result": null,"relayStatus": null},"subTaskStatus": [{"name": "test","stage": "Running","unit": "Sync","result": null,"unresolvedDDLLockID": "","sync": {"masterBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","masterBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-10","syncerBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","syncerBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-4","blockingDDLs": [],"unresolvedGroups": [],"synced": true,"binlogType": "remote","totalRows": "4","totalRps": "0","recentRps": "0"}}]}]}
可以看到任务运行正常，错误的 DDL 被跳过。
合库合表场景
假设现在存在如下四个上游表需要合并迁移到下游的同一个表 `shard_db`.`shard_table` ，任务模式为悲观协调模式：
- MySQL 实例 1 内有
shard_db_1库，包括shard_table_1和shard_table_2两个表。 - MySQL 实例 2 内有
shard_db_2库，包括shard_table_1和shard_table_2两个表。
初始时表结构为：
SHOW CREATE TABLE shard_db.shard_table;
+-------+-----------------------------------------------------------------------------------------------------------+| Table | Create Table |+-------+-----------------------------------------------------------------------------------------------------------+| tb | CREATE TABLE `shard_table` (`id` int(11) DEFAULT NULL,PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_bin |+-------+-----------------------------------------------------------------------------------------------------------+
此时，在上游所有分表上都执行以下 DDL 操作修改表字符集
ALTER TABLE `shard_db_*`.`shard_table_*` CHARACTER SET LATIN1 COLLATE LATIN1_DANISH_CI;
则会由于 TiDB 不支持该 DDL 语句而导致 DM 迁移任务中断，使用 query-status 命令可以看到 MySQL 实例 1 的 shard_db_1.shard_table_1 表和 MySQL 实例 2 的 shard_db_2.shard_table_1 表报错：
{"Message": "cannot track DDL: ALTER TABLE `shard_db_1`.`shard_table_1` CHARACTER SET UTF8 COLLATE UTF8_UNICODE_CI","RawCause": "[ddl:8200]Unsupported modify charset from latin1 to utf8"}
{"Message": "cannot track DDL: ALTER TABLE `shard_db_2`.`shard_table_1` CHARACTER SET UTF8 COLLATE UTF8_UNICODE_CI","RawCause": "[ddl:8200]Unsupported modify charset from latin1 to utf8"}
假设业务上可以接受下游 TiDB 不执行此 DDL 语句（即继续保持原有的表结构），则可以通过使用 binlog skip <task-name> 命令跳过该 DDL 语句以恢复迁移任务。操作步骤如下：
使用
binlog skip <task-name>跳过 MySQL 实例 1 和实例 2 当前错误的 DDL 语句» binlog skip test
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-01","worker": "worker1"},{"result": true,"msg": "","source": "mysql-replica-02","worker": "worker2"}]}
使用
query-status <task-name>查看任务状态，可以看到 MySQL 实例 1 的shard_db_1.shard_table_2表和 MySQL 实例 2 的shard_db_2.shard_table_2表报错：{"Message": "cannot track DDL: ALTER TABLE `shard_db_1`.`shard_table_2` CHARACTER SET UTF8 COLLATE UTF8_UNICODE_CI","RawCause": "[ddl:8200]Unsupported modify charset from latin1 to utf8"}
{"Message": "cannot track DDL: ALTER TABLE `shard_db_2`.`shard_table_2` CHARACTER SET UTF8 COLLATE UTF8_UNICODE_CI","RawCause": "[ddl:8200]Unsupported modify charset from latin1 to utf8"}
继续使用
binlog skip <task-name>跳过 MySQL 实例 1 和实例 2 当前错误的 DDL 语句» binlog skip test
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-01","worker": "worker1"},{"result": true,"msg": "","source": "mysql-replica-02","worker": "worker2"}]}
使用
query-status <task-name>查看任务状态» query-status test
执行结果
{"result": true,"msg": "","sources": [{"result": true,"msg": "","sourceStatus": {"source": "mysql-replica-01","worker": "worker1","result": null,"relayStatus": null},"subTaskStatus": [{"name": "test","stage": "Running","unit": "Sync","result": null,"unresolvedDDLLockID": "","sync": {"masterBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","masterBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-10","syncerBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","syncerBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-4","blockingDDLs": [],"unresolvedGroups": [],"synced": true,"binlogType": "remote","totalRows": "4","totalRps": "0","recentRps": "0"}}]},{"result": true,"msg": "","sourceStatus": {"source": "mysql-replica-02","worker": "worker2","result": null,"relayStatus": null},"subTaskStatus": [{"name": "test","stage": "Running","unit": "Sync","result": null,"unresolvedDDLLockID": "","sync": {"masterBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","masterBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-10","syncerBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","syncerBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-4","blockingDDLs": [],"unresolvedGroups": [],"synced": true,"binlogType": "remote","totalRows": "4","totalRps": "0","recentRps": "0"}}]}]}
可以看到任务运行正常，无错误信息。四条 DDL 全部被跳过。
迁移中断执行替代操作
如需在迁移中断时执行替代操作，可使用 binlog replace 命令：
binlog replace -h
replace the current error event or a specific binlog position (binlog-pos) with some ddlsUsage:dmctl binlog replace <task-name> <replace-sql1> <replace-sql2>... [flags]Flags:-h, --help help for replaceGlobal Flags:-b, --binlog-pos string position used to match binlog event if matched the binlog operation will be applied. The format like "mysql-bin|000001.000003:3270"-s, --source strings MySQL Source ID.
非合库合表场景
假设现在需要将上游的 db1.tbl1 表迁移到下游 TiDB，初始时表结构为：
SHOW CREATE TABLE db1.tbl1;
+-------+-----------------------------------------------------------------------------------------------------------+| Table | Create Table |+-------+-----------------------------------------------------------------------------------------------------------+| tb | CREATE TABLE `tbl1` (`id` int(11) DEFAULT NULL,PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_bin |+-------+-----------------------------------------------------------------------------------------------------------+
此时，上游执行以下 DDL 操作增加新列，并添加 UNIQUE 约束
ALTER TABLE `db1`.`tbl1` ADD COLUMN new_col INT UNIQUE;
则会由于 TiDB 不支持该 DDL 语句而导致 DM 迁移任务中断，使用 query-status 命令可看到如下错误：
{"Message": "cannot track DDL: ALTER TABLE `db1`.`tbl1` ADD COLUMN `new_col` INT UNIQUE KEY","RawCause": "[ddl:8200]unsupported add column 'new_col' constraint UNIQUE KEY when altering 'db1.tbl1'",}
我们将该 DDL 替换成两条等价的 DDL。操作步骤如下：
使用如下命令替换错误的 DDL 语句
» binlog replace test "ALTER TABLE `db1`.`tbl1` ADD COLUMN `new_col` INT;ALTER TABLE `db1`.`tbl1` ADD UNIQUE(`new_col`)";
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-01","worker": "worker1"}]}
使用
query-status <task-name>查看任务状态» query-status test
执行结果
{"result": true,"msg": "","sources": [{"result": true,"msg": "","sourceStatus": {"source": "mysql-replica-01","worker": "worker1","result": null,"relayStatus": null},"subTaskStatus": [{"name": "test","stage": "Running","unit": "Sync","result": null,"unresolvedDDLLockID": "","sync": {"masterBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","masterBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-10","syncerBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","syncerBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-4","blockingDDLs": [],"unresolvedGroups": [],"synced": true,"binlogType": "remote","totalRows": "4","totalRps": "0","recentRps": "0"}}]}]}
可以看到任务运行正常，错误的 DDL 已被替换且执行成功。
合库合表场景
假设现在存在如下四个上游表需要合并迁移到下游的同一个表 `shard_db`.`shard_table` ，任务模式为悲观协调模式：
- MySQL 实例 1 内有
shard_db_1库，包括shard_table_1和shard_table_2两个表。 - MySQL 实例 2 内有
shard_db_2库，包括shard_table_1和shard_table_2两个表。
初始时表结构为：
SHOW CREATE TABLE shard_db.shard_table;
+-------+-----------------------------------------------------------------------------------------------------------+| Table | Create Table |+-------+-----------------------------------------------------------------------------------------------------------+| tb | CREATE TABLE `shard_table` (`id` int(11) DEFAULT NULL,PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_bin |+-------+-----------------------------------------------------------------------------------------------------------+
此时，在上游所有分表上都执行以下 DDL 操作增加新列，并添加 UNIQUE 约束：
ALTER TABLE `shard_db_*`.`shard_table_*` ADD COLUMN new_col INT UNIQUE;
则会由于 TiDB 不支持该 DDL 语句而导致 DM 迁移任务中断，使用 query-status 命令可以看到 MySQL 实例 1 的 shard_db_1.shard_table_1 表和 MySQL 实例 2 的 shard_db_2.shard_table_1 表报错：
{"Message": "cannot track DDL: ALTER TABLE `shard_db_1`.`shard_table_1` ADD COLUMN `new_col` INT UNIQUE KEY","RawCause": "[ddl:8200]unsupported add column 'new_col' constraint UNIQUE KEY when altering 'shard_db_1.shard_table_1'",}
{"Message": "cannot track DDL: ALTER TABLE `shard_db_2`.`shard_table_1` ADD COLUMN `new_col` INT UNIQUE KEY","RawCause": "[ddl:8200]unsupported add column 'new_col' constraint UNIQUE KEY when altering 'shard_db_2.shard_table_1'",}
我们将该 DDL 替换成两条等价的 DDL。操作步骤如下：
使用如下命令分别替换 MySQL 实例 1 和实例 2 中错误的 DDL 语句
» binlog replace test -s mysql-replica-01 "ALTER TABLE `shard_db_1`.`shard_table_1` ADD COLUMN `new_col` INT;ALTER TABLE `shard_db_1`.`shard_table_1` ADD UNIQUE(`new_col`)";
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-01","worker": "worker1"}]}
» binlog replace test -s mysql-replica-02 "ALTER TABLE `shard_db_2`.`shard_table_1` ADD COLUMN `new_col` INT;ALTER TABLE `shard_db_2`.`shard_table_1` ADD UNIQUE(`new_col`)";
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-02","worker": "worker2"}]}
使用
query-status <task-name>查看任务状态，可以看到 MySQL 实例 1 的shard_db_1.shard_table_2表和 MySQL 实例 2 的shard_db_2.shard_table_2表报错：{"Message": "detect inconsistent DDL sequence from source ... ddls: [ALTER TABLE `shard_db`.`tb` ADD COLUMN `new_col` INT UNIQUE KEY] source: `shard_db_1`.`shard_table_2`], right DDL sequence should be ..."}
{"Message": "detect inconsistent DDL sequence from source ... ddls: [ALTER TABLE `shard_db`.`tb` ADD COLUMN `new_col` INT UNIQUE KEY] source: `shard_db_2`.`shard_table_2`], right DDL sequence should be ..."}
使用如下命令继续分别替换 MySQL 实例 1 和实例 2 中错误的 DDL 语句
» binlog replace test -s mysql-replica-01 "ALTER TABLE `shard_db_1`.`shard_table_2` ADD COLUMN `new_col` INT;ALTER TABLE `shard_db_1`.`shard_table_2` ADD UNIQUE(`new_col`)";
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-01","worker": "worker1"}]}
» binlog replace test -s mysql-replica-02 "ALTER TABLE `shard_db_2`.`shard_table_2` ADD COLUMN `new_col` INT;ALTER TABLE `shard_db_2`.`shard_table_2` ADD UNIQUE(`new_col`)";
{"result": true,"msg": "","sources": [{"result": true,"msg": "","source": "mysql-replica-02","worker": "worker2"}]}
使用
query-status <task-name>查看任务状态» query-status test
执行结果
{"result": true,"msg": "","sources": [{"result": true,"msg": "","sourceStatus": {"source": "mysql-replica-01","worker": "worker1","result": null,"relayStatus": null},"subTaskStatus": [{"name": "test","stage": "Running","unit": "Sync","result": null,"unresolvedDDLLockID": "","sync": {"masterBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","masterBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-10","syncerBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","syncerBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-4","blockingDDLs": [],"unresolvedGroups": [],"unresolvedGroups": [],"synced": true,"binlogType": "remote","totalRows": "4","totalRps": "0","recentRps": "0"}}]},{"result": true,"msg": "","sourceStatus": {"source": "mysql-replica-02","worker": "worker2","result": null,"relayStatus": null},"subTaskStatus": [{"name": "test","stage": "Running","unit": "Sync","result": null,"unresolvedDDLLockID": "","sync": {"masterBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","masterBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-10","syncerBinlog": "(DESKTOP-T561TSO-bin.000001, 2388)","syncerBinlogGtid": "143bdef3-dd4a-11ea-8b00-00155de45f57:1-4","blockingDDLs": [],"unresolvedGroups": [],"unresolvedGroups": [],"synced": try,"binlogType": "remote","totalRows": "4","totalRps": "0","recentRps": "0"}}]}]}
可以看到任务运行正常，无错误信息。四条 DDL 全部被替换。
其他命令
binlog 其他命令的使用，请参考上述 binlog skip、binlog replace 命令的使用方式。
