Migrate data from an RDS for MariaDB instance to an RDS for PostgreSQL instance - Data Transmission Service

Data Transmission Service (DTS) supports data migration from an RDS for MariaDB instance to an RDS for PostgreSQL instance.

Prerequisites

You have created a destination RDS for PostgreSQL instance. The storage space of the destination instance must be larger than the storage space used by the source RDS for MariaDB instance. For more information, see Create an RDS for PostgreSQL instance.
You have created a database in the destination RDS for PostgreSQL instance to store the migrated data. For more information, see Create accounts and databases.

Precautions

Note

During schema migration, DTS migrates foreign keys from the source database to the destination database.
During full data migration and incremental data migration, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade update and delete operations on the source database during data migration, data inconsistency may occur.

Type	Description
Source database limits	Bandwidth: The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. The tables to be migrated must have primary keys or UNIQUE constraints, and the fields in the keys or constraints must be unique. Otherwise, duplicate data may exist in the destination database. If you select tables as migration objects and need to edit them, such as mapping column names, a single data migration task supports a maximum of 1,000 tables. If you exceed this limit, a request error is reported after you submit the task. In this case, split the tables into multiple tasks or configure a task to migrate the entire database. If you perform incremental migration, binary logging (binlog) must meet the following requirements: Binary logging must be enabled. The binlog_format parameter must be set to row, and the binlog_row_image parameter must be set to full. Otherwise, an error is reported during the precheck and the data migration task cannot start. For an incremental migration task, DTS requires that the local binary logs of the source database are retained for more than 24 hours. For a task that includes both full and incremental migration, DTS requires that the local binary logs are retained for at least 7 days. After the full migration is complete, you can change the retention period to more than 24 hours. Otherwise, the task may fail because DTS cannot obtain the binary logs. In extreme cases, data may be inconsistent or lost. Issues that are caused by a binary log retention period shorter than the required period are not covered by the DTS Service-Level Agreement (SLA). During schema migration and full migration, do not perform DDL operations to change the schema of a database or table. Otherwise, the data migration task fails. Note During full migration, DTS queries the source database. This creates metadata locks, which may prevent DDL operations from being executed on the source database. If you perform only full data migration, do not write new data to the source database. Otherwise, data inconsistency occurs between the source and destination databases. To ensure real-time data consistency, select Schema Migration, Full Migration, and Incremental Migration. If the data to be migrated contains invisible columns, data loss may occur because the data in these columns cannot be obtained.
Other limits	Do not use tools such as pt-online-schema-change to perform online DDL operations on the migration objects in the source database. Otherwise, the migration fails. For columns of the FLOAT or DOUBLE data type, DTS reads the values using `ROUND(COLUMN,PRECISION)`. If you do not specify a precision, DTS uses a precision of 38 for the FLOAT data type and 308 for the DOUBLE data type. Confirm that the precision meets your business requirements. Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS consumes read and write resources of the source and destination databases, which may increase the database load. During full data migration, concurrent INSERT operations cause table fragmentation in the destination database. After full migration is complete, the table storage space in the destination database is larger than that in the source database. DTS attempts to resume a failed task within seven days. Before you switch your workloads to the destination instance, stop or release the task. You can also use the `REVOKE` command to revoke the write permissions of the database account that DTS uses to access the destination instance. This prevents the task from being automatically resumed, which would cause data in the source database to overwrite data in the destination instance. For a full migration or incremental migration task, if the tables to be migrated in the source database contain foreign keys, triggers, or event triggers, and the destination database account is a privileged account or an account with superuser permissions, DTS temporarily sets the session_replication_role parameter to replica at the session level during full or incremental migration. If the destination database account does not have this permission, you must manually set the session_replication_role parameter to replica in the destination database. During this period (when the session_replication_role parameter is set to replica during full or incremental migration), if there are cascade update or delete operations in the source database, data inconsistency may occur. After the DTS migration task is released, you can change the value of the session_replication_role parameter back to origin. If an instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, operations such as restarting the instance and adjusting parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters of the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters.

Billing

Migration type	Configuration Fees for Ingest Paths	Data transfer cost
Schema migration and full data migration	Free of charge.	You are charged for data transfer if you migrate data out of Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Schema migration
DTS migrates the schema definitions of the migration objects from the source database to the destination database.
Full migration
DTS migrates all historical data of the migration objects from the source database to the destination database.
Incremental migration
After full migration, DTS migrates incremental data updates from the source database to the destination database. Incremental data migration lets you smoothly migrate data without interrupting your applications.

SQL operations that can be incrementally migrated

Operation type	SQL operation
DML	INSERT, UPDATE, DELETE

Permissions required for database accounts

Database	Schema migration	Full migration	Incremental migration
RDS for MariaDB instance	SELECT permission	SELECT permission	REPLICATION CLIENT, REPLICATION SLAVE, SHOW VIEW, and SELECT
RDS for PostgreSQL	CREATE and USAGE on the migration objects	Owner of the schema	Owner of the schema

To create and grant permissions to a database account:

For an RDS for MariaDB instance, see Create an account and Modify or reset account permissions.
For an RDS for PostgreSQL instance, see Create an account and Authorize a service account.

Procedure

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.
Optional. Click New Configuration Page in the upper-right corner of the page.
Note
- Skip this step if the Back to Previous Version button is displayed in the upper-right corner of the page.
- Specific parameters in the new and previous versions of the configuration page may be different. We recommend that you use the new version of the configuration page.

Configure the source and destination databases. The following table describes the parameters.

Category	Configuration	Description
None	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
Source Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select MariaDB.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the source RDS for MariaDB instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance of the current Alibaba Cloud account is used. Select No.
	Instance ID	Select the ID of the source RDS for MariaDB instance.
	Database Account	Enter the database account of the source RDS for MariaDB instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.
	Encryption	The default connection method for an RDS for MariaDB instance is Non-encrypted Connection.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select PostgreSQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the destination RDS for PostgreSQL instance resides.
	Instance ID	Select the ID of the destination RDS for PostgreSQL instance.
	Database Name	Enter the name of the database in the destination RDS for PostgreSQL instance that will store the migrated objects.
	Database Account	Enter the database account of the destination RDS for PostgreSQL instance.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the source database. You can configure this parameter based on your business requirements. In this example, Non-encrypted is selected. If you want to establish an SSL-encrypted connection to the source database, perform the following steps: Select SSL-encrypted, upload CA Certificate, Client Certificate, and Private Key of Client Certificate as needed, and then specify Private Key Password of Client Certificate. Note If you set Encryption to SSL-encrypted for a self-managed PostgreSQL database, you must upload CA Certificate. If you want to use the client certificate, you must upload Client Certificate and Private Key of Client Certificate and specify Private Key Password of Client Certificate. For information about how to configure SSL encryption for an ApsaraDB RDS for PostgreSQL instance, see SSL encryption.

In the lower part of the page, click Test Connectivity and Proceed.
Note
- Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be migrated.

On the Configure Objects page, configure the objects that you want to migrate.

Configuration	Description
Migration Types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you do not select Schema Migration, make sure a database and a table are created in the destination database to receive data and the object name mapping feature is enabled in Selected Objects. If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are migrated to the destination database. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select objects at the database, table, and column levels.
Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note If you use the object name mapping feature, other objects that depend on the mapped object may fail to be migrated. To set a WHERE clause to filter data, right-click the table to be migrated in the Selected Objects box and set the filter condition in the dialog box that appears. For more information, see Set filter conditions. To select the SQL operations to be migrated at the database or table level, right-click the migration object in the Selected Objects box and select the desired SQL operations in the dialog box that appears.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1,440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	You can select an environment tag for the instance. In this example, no tag is selected.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

Purchase the instance.

Wait until Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.