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zh: update "safe mode" (#444) #450

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Oct 28, 2020
Merged

zh: update "safe mode" (#444) #450

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f5eae26
cherry pick #444 to release-2.0
lance6716 Oct 27, 2020
2ba3de2
Merge branch 'release-2.0' into release-2.0-6c8c5487f0dd
ti-srebot Oct 28, 2020
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8 changes: 6 additions & 2 deletions zh/glossary.md
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Expand Up @@ -94,9 +94,13 @@ DM-worker 内部用于从上游拉取 Binlog 并写入数据到 Relay log 的处

### Safe mode

指增量复制过程中，用于支持在表结构中存在主键或唯一索引的条件下可重复导入 DML 的模式。
指增量复制过程中，用于支持在表结构中存在主键或唯一索引的条件下可重复导入 DML 的模式。该模式的主要特点是：将来自上游的 `INSERT` 改写为 `REPLACE`，将 `UPDATE` 改写为 `DELETE` 与 `REPLACE` 后再向下游执行。

该模式的主要特点为将来自上游的 `INSERT` 改写为 `REPLACE`，将 `UPDATE` 改写为 `DELETE` 与 `REPLACE` 后再向下游执行。在启动或恢复增量复制任务的前 5 分钟 TiDB DM 会自动启动 Safe mode，另外也可以在任务配置文件中通过 `safe-mode` 参数手动开启。
该模式会在满足如下任一条件时启用：

- 启动或恢复增量复制任务的前 5 分钟保持启用
- 任务配置文件中设置 `safe-mode: true` 时会始终启用
- 在全量迁移任务中的 dump 处理单元配置 `--consistency none` 后，不能确定导出开始时的 binlog 变动是否影响了导出数据。Safe mode 会在增量复制这部分 binlog 时保持启用

### Shard DDL

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2 changes: 1 addition & 1 deletion zh/migrate-from-mysql-aurora.md
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Expand Up @@ -186,7 +186,7 @@ tiup dmctl --master-addr 127.0.0.1:8261 operate-source create dm-test/source2.ya

> **注意：**
>
> 由于 Aurora 不支持 FTWRL，仅使用全量模式导出数据时需要暂停写入，参见 [AWS 官网说明](https://aws.amazon.com/cn/premiumsupport/knowledge-center/mysqldump-error-rds-mysql-mariadb/)。在示例的全量+增量模式下，DM 将自动启用 `safe mode` 解决这一问题。在其他模式下如需保证数据一致，参见 [AWS 官网说明](https://aws.amazon.com/cn/premiumsupport/knowledge-center/mysqldump-error-rds-mysql-mariadb/)操作。
> 由于 Aurora 不支持 FTWRL，仅使用全量模式导出数据时需要暂停写入，参见 [AWS 官网说明](https://aws.amazon.com/cn/premiumsupport/knowledge-center/mysqldump-error-rds-mysql-mariadb/)。在示例的全量+增量模式下，DM 将自动启用 [`safe mode`](glossary.md#safe-mode) 解决这一问题。在其他模式下如需保证数据一致，参见 [AWS 官网说明](https://aws.amazon.com/cn/premiumsupport/knowledge-center/mysqldump-error-rds-mysql-mariadb/)操作。

本示例选择迁移 Aurora 已有数据并将新增数据实时迁移给 TiDB，即**全量+增量**模式。根据上文的 TiDB 集群信息、已添加的 `source-id`、要迁移的表，保存如下任务配置文件 `task.yaml`：

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