tools/dm: update manage-task.md and add precheck.md (#931)

* tools/dm: update manage-task.md and add precheck.md

Via: pingcap/docs-cn#1139

* dm: update the links related to precheck.md

* dm: address lilian's comments

tools/dm/manage-task.md

@@ -82,59 +82,6 @@ Flags:
 # Use "dmctl [command] --help" for more information about a command.
 ```
 
-## Precheck the upstream MySQL instance configuration
-
-To detect possible errors of data synchronization configuration in advance, DM provides the precheck feature. You can use the `check-task` command to precheck whether the upstream MySQL instance configuration satisfies the DM requirements.
-
-The user of the upstream and downstream databases must have the corresponding read and write privileges. DM checks the following privileges and configuration automatically while starting the data synchronization task:
-
-+ Database version
-
-    - 5.5 < MySQL version < 5.8
-    - MariaDB version >= 10.1.2
-
-+ MySQL binlog configuration
-
-    - Whether the binlog is enabled (DM requires that the binlog must be enabled)
-    - Whether `binlog_format=ROW` (DM only supports the binlog synchronization in the ROW format)
-    - Whether `binlog_row_image=FULL` (DM only supports `binlog_row_image=FULL`)
-
-+ The privileges of the upstream MySQL instance user
-
-    The MySQL user in DM configuration needs to have the following privileges at least:
-
-    - REPLICATION SLAVE
-    - REPLICATION CLIENT
-    - RELOAD
-    - SELECT
-
-+ The compatibility of the upstream MySQL table schema
-
-    TiDB differs from MySQL in compatibility in the following aspects:
-
-    - Does not support the foreign key
-    - [Character set compatibility differs](/sql/character-set-support.md)
-
-+ The consistency check on the upstream MySQL multiple-instance shards
-
-    + The schema consistency of all sharded tables
-
-        - Column size
-        - Column name
-        - Column position
-        - Column type
-        - Primary key
-        - Unique index
-
-    + The conflict of the auto increment primary keys in the sharded tables
-
-        - The check fails in the following two conditions:
-
-            - The auto increment primary key exists in the sharded tables and its column type *is not* bigint.
-            - The auto increment primary key exists in the sharded tables and its column type *is* bigint, but column mapping *is not* configured.
-
-        - The check succeeds in other conditions except the two above.
-
 ## Manage the data synchronization task
 
 This section describes how to use the task management commands to execute the following operations:

tools/dm/overview.md

@@ -77,7 +77,7 @@ Before using the DM tool, note the following restrictions:
     - 5.5 < MySQL version < 5.8
     - MariaDB version >= 10.1.2
 
-    Data Migration [prechecks the corresponding privileges and configuration automatically](/tools/dm/manage-task.md#precheck-the-upstream-mysql-instance-configuration) while starting the data synchronization task using dmctl.
+    Data Migration [prechecks the corresponding privileges and configuration automatically](/tools/dm/precheck.md) while starting the data synchronization task using dmctl.
 
 + DDL syntax
 

tools/dm/practice.md

@@ -111,7 +111,7 @@ To detect possible errors of data synchronization configuration in advance, DM p
 - DM automatically checks the corresponding privileges and configuration while starting the data synchronization task.
 - You can also use the `check-task` command to manually precheck whether the upstream MySQL instance configuration satisfies the DM requirements.
 
-For details about the precheck feature, see [Precheck the upstream MySQL instance configuration](/tools/dm/manage-task.md#precheck-the-upstream-mysql-instance-configuration).
+For details about the precheck feature, see [Precheck the upstream MySQL instance configuration](/tools/dm/precheck.md).
 
 > **Note:** Before starting the data synchronization task for the first time, you should have got the upstream configured. Otherwise, an error is reported while you start the task.
 

tools/dm/precheck.md

@@ -0,0 +1,64 @@
+---
+title: Precheck the upstream MySQL instance configuration
+summary: Use the precheck feature provided by DM to detect errors in the upstream MySQL instance configuration.
+category: tools
+---
+
+# Precheck the upstream MySQL instance configuration
+
+This document introduces the precheck feature provided by DM. This feature is used to detect possible errors in the upstream MySQL instance configuration when the data replication task is started.
+
+## Command
+
+`check-task` allows you to precheck whether the upstream MySQL instance configuration satisfies the DM requirements. 
+
+## Checking items
+
+Upstream and downstream database users must have the corresponding read and write privileges. DM checks the following privileges and configuration automatically while the data replication task is started:
+
++ Database version
+
+    - 5.5 < MySQL version < 5.8
+    - MariaDB version >= 10.1.2
+
++ MySQL binlog configuration
+
+    - Whether the binlog is enabled (DM requires that the binlog must be enabled)
+    - Whether `binlog_format=ROW` (DM only supports replication of the binlog in the ROW format)
+    - Whether `binlog_row_image=FULL` (DM only supports `binlog_row_image=FULL`)
+
++ The privileges of the upstream MySQL instance users
+
+    MySQL users in DM configuration need to have the following privileges at least:
+
+    - REPLICATION SLAVE
+    - REPLICATION CLIENT
+    - RELOAD
+    - SELECT
+
++ The compatibility of the upstream MySQL table schema
+
+    TiDB differs from MySQL in compatibility in the following aspects:
+
+    - TiDB does not support the foreign key.
+    - [Character set compatibility differs](/sql/character-set-support.md).
+
++ The consistency of the sharded tables in the multiple upstream MySQL instances
+
+    + The schema consistency of all sharded tables
+
+        - Column size
+        - Column name
+        - Column position
+        - Column type
+        - Primary key
+        - Unique index
+
+    + The conflict of the auto increment primary keys in the sharded tables
+
+        - The check fails in the following two conditions:
+
+            - The auto increment primary key exists in the sharded tables and its column type *is not* bigint.
+            - The auto increment primary key exists in the sharded tables and its column type *is* bigint, but column mapping *is not* configured.
+
+        - The check succeeds in other conditions except the two above.

tools/dm/troubleshooting.md

@@ -28,7 +28,7 @@ However, you need to reset the data synchronization task in some cases. For deta
 
 For database related passwords in all the DM configuration files, use the passwords encrypted by `dmctl`. If a database password is empty, it is unnecessary to encrypt it. For how to encrypt the plaintext password, see [Encrypt the upstream MySQL user password using dmctl](/tools/dm/deployment.md#encrypt-the-upstream-mysql-user-password-using-dmctl).
 
-In addition, the user of the upstream and downstream databases must have the corresponding read and write privileges. Data Migration also [prechecks the corresponding privileges automatically](/tools/dm/manage-task.md#precheck-the-upstream-mysql-instance-configuration) while starting the data synchronization task.
+In addition, the user of the upstream and downstream databases must have the corresponding read and write privileges. Data Migration also [prechecks the corresponding privileges automatically](/tools/dm/precheck.md) while starting the data synchronization task.
 
 ### Incompatible DDL statements