处理出错的 SQL 语句

本文介绍了如何使用 DM 来处理出错的 SQL 语句。

目前,TiDB 并不完全兼容所有的 MySQL 语法(详见 TiDB 已支持的 DDL 语句)。当使用 DM 从 MySQL 迁移数据到 TiDB 时,如果 TiDB 不支持对应的 SQL 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 handle-error 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,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 handle-error <task-name> skip 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 handle-error <task-name> replace 替代该 DDL 的迁移以恢复迁移任务。

命令介绍

使用 dmctl 手动处理出错的 SQL 语句时,主要使用的命令包括 query-statushandle-error

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

handle-error

handle-error 命令用于处理错误的 sql 语句。

命令用法

» handle-error -h
Usage:
  dmctl handle-error <task-name | task-file> [-s source ...] [-b binlog-pos] <skip/replace/revert> [replace-sql1;replace-sql2;] [flags]

Flags:
  -b, --binlog-pos string   position used to match binlog event if matched the handler-error operation will be applied. The format like "mysql-bin|000001.000003:3270"
  -h, --help                help for handle-error

Global Flags:
  -s, --source strings   MySQL Source ID

参数解释

  • task-name

    • 非 flag 参数,string,必选;
    • 指定预设的操作将生效的任务。
  • source

    • flag 参数,string,--source
    • source 指定预设操作将生效的 MySQL 实例。
  • skip:跳过该错误

  • replace:替代错误的 DDL 语句

  • revert:重置该错误先前的 skip/replace 操作, 仅在先前的操作没有最终生效前执行

  • binlog-pos

    • flag 参数,string,--binlog-pos
    • 若不指定,DM 会自动处理当前出错的 SQL 语句
    • 在指定时表示操作将在 binlog-pos 与 binlog event 的 position 匹配时生效,格式为 binlog-filename:binlog-pos,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。

使用示例

迁移中断执行跳过操作

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 handle-error <task-name> skip 命令跳过该 DDL 语句以恢复迁移任务。操作步骤如下:

  1. 使用 handle-error <task-name> skip 跳过当前错误的 DDL 语句

    » handle-error test skip
    {
        "result": true,
        "msg": "",
        "sources": [
            {
                "result": true,
                "msg": "",
                "source": "mysql-replica-01",
                "worker": "worker1"
            }
        ]
    }
  2. 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": {
                            "totalEvents": "4",
                            "totalTps": "0",
                            "recentTps": "0",
                            "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"
                        }
                    }
                ]
            }
        ]
    }

    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_1shard_table_2 两个表。
  • MySQL 实例 2 内有 shard_db_2 库,包括 shard_table_1shard_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 handle-error <task-name> skip 命令跳过该 DDL 语句以恢复迁移任务。操作步骤如下:

  1. 使用 handle-error <task-name> skip 跳过 MySQL 实例 1 和实例 2 当前错误的 DDL 语句

    » handle-error test skip
    {
        "result": true,
        "msg": "",
        "sources": [
            {
                "result": true,
                "msg": "",
                "source": "mysql-replica-01",
                "worker": "worker1"
            },
            {
                "result": true,
                "msg": "",
                "source": "mysql-replica-02",
                "worker": "worker2"
            }
        ]
    }
  2. 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"
    }
  3. 继续使用 handle-error <task-name> skip 跳过 MySQL 实例 1 和实例 2 当前错误的 DDL 语句

    » handle-error test skip
    {
        "result": true,
        "msg": "",
        "sources": [
            {
                "result": true,
                "msg": "",
                "source": "mysql-replica-01",
                "worker": "worker1"
            },
            {
                "result": true,
                "msg": "",
                "source": "mysql-replica-02",
                "worker": "worker2"
            }
        ]
    }
  4. 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": {
                            "totalEvents": "4",
                            "totalTps": "0",
                            "recentTps": "0",
                            "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"
                        }
                    }
                ]
            },
            {
                "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": {
                            "totalEvents": "4",
                            "totalTps": "0",
                            "recentTps": "0",
                            "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"
                        }
                    }
                ]
            }
        ]
    }

    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

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:

  1. 使用如下命令替换错误的 DDL 语句

    » handle-error test replace "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"
            }
        ]
    }
  2. 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": {
                            "totalEvents": "4",
                            "totalTps": "0",
                            "recentTps": "0",
                            "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"
                        }
                    }
                ]
            }
        ]
    }

    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_1shard_table_2 两个表。
  • MySQL 实例 2 内有 shard_db_2 库,包括 shard_table_1shard_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:

  1. 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

    » handle-error test -s mysql-replica-01 replace "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"
            }
        ]
    }
    » handle-error test -s mysql-replica-02 replace "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"
            }
        ]
    }
  2. 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 ..."
    }
  3. 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

    » handle-error test -s mysql-replica-01 replace "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"
            }
        ]
    }
    » handle-error test -s mysql-replica-02 replace "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"
            }
        ]
    }
  4. 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": {
                            "totalEvents": "4",
                            "totalTps": "0",
                            "recentTps": "0",
                            "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"
                        }
                    }
                ]
            },
            {
                "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": {
                            "totalEvents": "4",
                            "totalTps": "0",
                            "recentTps": "0",
                            "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"
                        }
                    }
                ]
            }
        ]
    }

    可以看到任务运行正常,无错误信息。四条 DDL 全部被替换。