---
title: "Troubleshoot common issues"
slug: "dms-troubleshot-common"
updated: 2026-10-08T07:10:43Z
published: 2026-10-08T07:10:43Z
canonical: "guide.ncloud-docs.com/dms-troubleshot-common"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://guide.ncloud-docs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Troubleshoot common issues

Available in VPC

You might run into the following problems when using Database Migration Service. Find out causes and possible solutions.

## Migration error

Test Connection and migration failed.

#### Cause

- No Database in source DB.
- Target DB has the same Database name as source DB.
- Permissions required for migration have not been set.
- Settings to apply to source DB have not been applied.
- MyISAM, BLACKHOLE, FEDERATED, and ARCHIVE engines are not supported.
- Character sets of source DB and target DB are different.
- Target DB has been assigned to the cluster in service.

#### Solution

- Check if there is at least 1 Database in source DB.
- Delete duplicate Database.
- Check if source DB is in GTID mode. For permissions items needed for migration, see [minimum permissions required for migration](/docs/en/dms-connect#%EB%A7%88%EC%9D%B4%EA%B7%B8%EB%A0%88%EC%9D%B4%EC%85%98%EC%9D%84%EC%9C%84%ED%95%9C%EC%B5%9C%EC%86%8C%EA%B6%8C%ED%95%9C%ED%95%84%EC%9A%94%ED%95%AD%EB%AA%A9).
- Check following settings are applied to source DB:
  - Activate binary logs and assign `server_id` value.
  - Check whether the value of `log_bin` is displayed as `ON`.
  - For more information on preparations required for source DB replication, see [preparations](/docs/en/dms-connect#1%EC%82%AC%EC%A0%84%EC%A4%80%EB%B9%841).
- Check if you selected MySQL engine that is not supported. To check whether migration is supported depending on the detailed settings of source DB, see [supported databases](/docs/en/dms-spec#%EC%A7%80%EC%9B%90%EB%8D%B0%EC%9D%B4%ED%84%B0%EB%B2%A0%EC%9D%B4%EC%8A%A4).
- The supported character sets for migration are utf8, utf8mb4, euckr. If the character set is different, change character set of DB and table character set of source DB and proceed with migration.
- Target DB restarts during migration and is only available for reading data. Make sure not to designate a currently operating cluster as your target DB.

## Migration incomplete

All migration steps, including replication, have been completed, but the status is displayed as "migration" in the Cloud DB for MySQL console.

#### Cause

In migration completed (same as replication completed) stage, DB Service migration is finally available only by clicking **[Complete]** in the console.

#### Solution

After checking the status becomes "Migration Completed", click **[Complete]**.

## MariaDB migration

Compatibility error messages appear during MariaDB migration.

#### Cause

Migration is available even when the source DB is MariaDB. However, MariaDB version that reached EOL can cause compatibility-related error messages during migration.

#### Solution

If the same error occurs continuously, change the target DB to MySQL version 5.7 to proceed with the migration or change the version of the source DB.

## Migration error on definer account set in source DB

The definer account that is set in the source DB was not automatically created during migration.

#### Cause

User accounts are not included in the migration target.

#### Solution

Create an account used in the definer in the target DB directly. For more information, see [manage DB user](/docs/en/database-database-5-2#DBUser%EA%B4%80%EB%A6%AC).

## DB Config settings not migrated

DB Config settings were not migrated.

#### Cause

Migration for DB Config settings is not supported.

#### Solution

Set them the same as those for source DB on target DB such as the character set/collation.

## Test Connection delay

Test connection takes too much time.

#### Cause

The process may take a few minutes if there is a large number of source DB schemas. It is a procedure to check authorization and inspect schema for the normal operation of migration.

#### Solution

No action is required as it is not an error. Make sure not to refresh as the check process will be reset.

## "Killed $RESTORECMD" error message

Backup type: "Killed $RESTORECMD" error popup appears when using mydumper.

#### Cause

For a large target table, a higher thread limit results in higher memory utilization during the import process. This increases the likelihood of OOM kills or server hangs.

#### Solution

Try again by lowering Thread limit after deleting migration.

## Permission error

- Error occurs when executing `GRANT REPLICATION SLAVE ON . TO '계정명'@'허용호스트';` I received the message **[28000][1045] Access denied for user 'account name'@'allowed host'** as well.
- I recieved the message **Master command COM_REGISTER_SLAVE failed: Access denied for user 'account name'@'allowed host' (using password: YES) (Errno: 1045)**.

#### Cause

- If there is a problem with permissions of the account you are using, you may get an error.
- If there is no permission for replication, error may occur.
- Some of the required privileges have not been granted to the migration account. The required privileges vary depending on the backup method (mysqldump or mydumper), the target DB version, and whether GTID mode is enabled. (Error code: 1044, 1142, 1227)

#### Solution

Check permissions of the account you are using. To run the commands, the account should have a permission for `GRANT REPLICATION SLAVE*.* TO '계정명'@'허용호스트' WITH GRANT OPTION ;` The permission is for DDL and is only granted to accounts created from the console.

**Grant REPLICATION permissions**

1. Enter the following commands in source DB to check REPLICATION SLAVE permissions:

```
show grants for 'account name'@'allowed host';`
```
2. Grant REPLICATION SLAVE permission to accounts in source DB.

```
GRANT REPLICATION SLAVE ON *.* TO 'account name'@'allowed host';`
```

**Check migration permissions** Verify that all required privileges corresponding to the selected backup method and version have been granted. For more information, see [minimum permissions required for migration](/docs/en/dms-connect#%EB%A7%88%EC%9D%B4%EA%B7%B8%EB%A0%88%EC%9D%B4%EC%85%98%EC%9D%84%EC%9C%84%ED%95%9C%EC%B5%9C%EC%86%8C%EA%B6%8C%ED%95%9C%ED%95%84%EC%9A%94%ED%95%AD%EB%AA%A9).

## Precautions for migrating some databases

If you proceed with the migration for only some databases, certain cross-database SQL operations may not be replicated or may result in errors during execution. To prevent data consistency issues or execution errors after migration, review your application logic based on the following information.

#### Cause

- If cross-database SQL is used, execution errors may occur due to databases that are not included in the migration target.

#### Solution

- If cross-database SQL is used, make sure to include all related databases in the migration target.

1. Test environment

- Database to migrate: mig-db
- Database to exclude from migration: non-mig-db
- A replication filter example is as follows:

```
REPLICATE_WILD_IGNORE_TABLE = ('mysql.*', 'non-mig-db.*')
```

1. Replication behavior criteria  

Replication behavior varies depending on the SQL statement type. Refer to the following criteria.

| Type | Replication criteria | Description |
| --- | --- | --- |
| DML (INSERT/UPDATE/DELETE) | Based on target table (DB) | Replication occurs when the target table is included in the target DB |
| DDL (CREATE/ALTER/DROP) | Based on target object (DB) | Replication occurs when the created/edited/dropped object belongs to the target database |
| Procedure/function/view | Based on definition location (DB) | Replication occurs if defined in the target database |
| Cross-DB operations | May cause execution errors | Replication is possible, but if the excluded DB is not available, execution errors may occur |

1. Key scenarios

              Note

              

**Not replicated** means the target DB was excluded from replication, thus it is not a replication error

3.1. DML (data manipulation)

| SQL example | Replication |
| --- | --- |
| USE mig-db; INSERT INTO non-mig-db.table | Not replicated |
| USE non-mig-db; INSERT INTO mig-db.table | Replicated |
| USE mig-db; DELETE FROM mig-db.orders JOIN non-mig-db.table | Partial failure possible (non-mig-db access error) |

              Caution

              

- Replication may be omitted or execution errors may occur when an excluded DB is referenced or included in a join.
- Avoid cross-DB DML operations whenever possible.

3.2. DDL (create/edit/delete table)

| SQL example | Replication |
| --- | --- |
| USE mig-db; CREATE/ALTER/DROP TABLE non-mig-db.table | Not replicated |
| USE non-mig-db; CREATE/ALTER/DROP TABLE mig-db.table | Replicated |

3.3. View

| SQL example | Replication (mysqldump) | Replication (mydumper) | Upon execution |
| --- | --- | --- | --- |
| USE mig-db; CREATE VIEW ... JOIN non-mig-db.table | Replicated | Not migrated | Error occurs if excluded DB is not present |
| USE non-mig-db; CREATE VIEW ... | Not replicated | Not migrated | - |

              Caution

              

- Referencing an excluded DB in a view definition may cause execution errors.
- It is recommended to define views based on a single DB.
- Whether a view is included in migration depends on the backup method:
  - When using **mysqldump**: View is included in migration
  - When using **mydumper**: View is not included in migration

3.4. Stored Procedure/Function/Trigger

| SQL example | Replication | Upon execution |
| --- | --- | --- |
| Inside mig-db.CrossDbDataSync(), INSERT INTO non-mig-db.table | Replicated | May cause execution errors |
| non-mig-db.LogUserActivity() | Not replicated | - |
| USE mig-db; CREATE TRIGGER ... INSERT INTO non-mig-db.table | Replicated | May cause execution errors |

              Caution

              

- Although the object is replicated, errors may occur during execution due to access to excluded DBs.
- It is recommended to define all objects based on a single DB.

              Note

              

- Replication is determined based on the actual target DB of the operation, not the current execution DB (USE).
- Avoid cross-DB operations whenever possible.
  - Referencing or joining an excluded DB may result in execution errors.
  - If cross-DB SQL is included, ensure all related DBs are included in the migration target.
- Define procedures, functions, triggers, and views based on a single DB and avoid referencing excluded DBs.
- Test application logic in advance to prevent execution errors after migration.