Migrate data from a PolarDB for PostgreSQL(Compatible with Oracle) cluster to a self-managed Oracle database - Data Transmission Service

This topic describes how to migrate data from a PolarDB for PostgreSQL (Compatible with Oracle) cluster to a self-managed Oracle database by using Data Transmission Service (DTS).

Prerequisites

The source PolarDB for PostgreSQL (Compatible with Oracle) cluster is created. For more information, see Create a PolarDB for PostgreSQL(Compatible with Oracle) cluster.
The value of the wal_level parameter is set to logical for the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. This setting ensures that logical encoding is supported in write-ahead logging (WAL). For more information, see Configure cluster parameters.

Limits

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 and delete operations on the source database during data migration, data inconsistency may occur.

Category	Description
Limits on the source database	The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The tables to be migrated must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If you select tables as objects that you want to migrate and you need to edit tables, such as renaming tables or columns in the destination database, up to 1,000 tables can be migrated in a single data migration task. If you run a task to migrate more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables or configure a task to migrate the entire database. If you need to migrate incremental data, make sure that the following requirements are met: The write-ahead logging (WAL) feature must be enabled. For incremental data migration, the WAL logs of the source database must be stored for more than 24 hours. For full data and incremental data migration, the WAL logs of the source database must be stored for at least seven days. Otherwise, DTS may fail to obtain the WAL logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After full data migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of WAL logs based on the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed. Limits on operations to be performed on the source database: During full data migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails. If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data inconsistency between the source and destination databases occurs. To ensure data consistency, we recommend that you select Full Data Migration and Incremental Data Migration as the migration types. If you want to perform a primary/secondary switchover on the source PolarDB for PostgreSQL(Compatible with Oracle) cluster, the Logical Replication Slot Failover feature must be enabled. This prevents logical subscriptions from being interrupted and ensures that your data synchronization task can run as expected. For more information, see Logical replication slot failover. If one or more long-running transactions exist in the source database and incremental data is migrated in the data migration task, the WAL logs generated before the long-running transactions in the source database are committed may be accumulated. As a result, the disk space of the source database may be insufficient.
Other limits	Schema migration is not supported. Before you configure a data migration task, you must create databases and tables in the destination instance based on the databases and tables that you want to migrate. A data migration task can migrate data from only a single database. To migrate data from multiple databases, you must create a data migration task for each database. During incremental data migration, if you select a schema as the object to be migrated, take note of the following limits: If you create a table in the schema or run the RENAME command to rename the table, you must execute the `ALTER TABLE schema.table REPLICA IDENTITY FULL;` statement before you write data to the table. Note Replace the `schema` and `table` in the preceding sample statement with the actual schema name and table name. To ensure the accuracy of the displayed latency during incremental data migration, DTS creates a table named `dts_postgres_heartbeat` in the source database. The following figure shows the structure and content of the table. During incremental data migration, DTS creates a replication slot for the source database. The replication slot is prefixed with `dts_sync_`. DTS can obtain the incremental logs of the source database within the last 15 minutes by using this replication slot. Note After the DTS instance is released, the replication slot is automatically deleted. If you change the password of the source database or delete the IP address whitelist of DTS, the replication slot cannot be automatically deleted. In that case, you must manually delete the replication slot from the source database to prevent the replication slot from piling up. If the data migration task is released or fails, DTS automatically clears the replication slot. If a primary/secondary switchover is performed on the source cluster, you must log on to the secondary instance to clear the replication slot. During incremental data migration, DTS creates a replication slot for the source database. The replication slot is prefixed with `dts_sync_`. DTS can obtain the incremental logs of the source database within the last 15 minutes by using this replication slot. Note After the DTS instance is released, the replication slot is automatically deleted. If you change the password of the source database or delete the IP address whitelist of DTS, the replication slot cannot be automatically deleted. In that case, you must manually delete the replication slot from the source database to prevent the replication slot from piling up. If the data migration task is released or fails, DTS automatically clears the replication slot. If a primary/secondary switchover is performed on the source cluster, you must log on to the secondary instance to clear the replication slot. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is complete, the tablespace of the destination database is larger than that of the source database. Make sure that the precision settings for columns of the FLOAT or DOUBLE data type meet your business requirements. DTS uses the `ROUND(COLUMN,PRECISION)` function to retrieve values from columns of the FLOAT or DOUBLE data type. If you do not specify a precision, DTS sets the precision for the FLOAT data type to 38 digits and the precision for the DOUBLE data type to 308 digits. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination database, you must stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination database after the failed task is resumed.
Special cases	If the self-managed Oracle database is deployed in a Real Application Cluster (RAC) architecture and is connected to DTS over an Alibaba Cloud virtual private cloud (VPC), you must connect the Single Client Access Name (SCAN) IP address of the Oracle RAC and the virtual IP address (VIP) of each node to the VPC and configure routes. The settings ensure that your DTS task can run as expected. For more information, see Connect an on-premises database to Alibaba Cloud and Connect a data center to DTS by using VPN Gateway. Important When you configure the self-managed Oracle database in the DTS console, you must specify the SCAN IP address of the Oracle RAC as the database endpoint or IP address.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Full data migration	Free of charge.	Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Migration type	Description
Full data migration	DTS migrates the historical data of objects from the source database to the destination database. Note During full data migration, we recommend that you do not perform DDL operations on the objects to be migrated. Otherwise, the objects may fail to be migrated.
Incremental data migration	DTS retrieves redo log files from the source database. Then, DTS migrates incremental data from the source database to the destination database. Incremental data migration ensures service continuity when you migrate data.

SQL operations that can be incrementally migrated

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	DDL operations can be migrated only in the data migration tasks that are created after October 1, 2020. Important If a data migration task is created before May 12, 2023, you must create a trigger and a function in the source database to capture DDL information before you configure the data migration task. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases. Incremental data migration does not support the data of the BIT type. If the account of the source database is a privileged account, DTS can migrate the following DDL statements: CREATE TABLE and DROP TABLE ALTER TABLE, including RENAME TABLE, ADD COLUMN, ADD COLUMN DEFAULT, ALTER COLUMN TYPE, DROP COLUMN, ADD CONSTRAINT, ADD CONSTRAINT CHECK, and ALTER COLUMN DROP DEFAULT TRUNCATE TABLE CREATE INDEX ON TABLE Important You cannot migrate additional information of DDL statements, such as CASCADE or RESTRICT. You cannot migrate the DDL statements from a session for which the `SET session_replication_role = replica` command is executed. If the SQL statements submitted by the source database at a time contain both DML and DDL statements, DTS does not migrate the DDL statements. If the SQL statements submitted by the source database at a time contain DDL statements on objects not to be migrated, DTS does not migrate the DDL statements.

Permissions required for database accounts

Database	Required permission
Source PolarDB for PostgreSQL (Compatible with Oracle) cluster	Permissions of a privileged account
Self-managed Oracle database	Permissions of the schema owner

For more information about how to create a database account and grant permissions to the account, see the following topics:

PolarDB for PostgreSQL (Compatible with Oracle) cluster: Create database accounts
Self-managed Oracle databases: CREATE USER and GRANT

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
Note
- Operations 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.
- You can also go to the Data Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. In the Create Task wizard, configure the source and destination databases.

Warning

After you configure the source and destination databases, we recommend that you read the limits that are displayed in the upper part of the page. Otherwise, the task may fail or data inconsistency may occur.

Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically assigns a name to the task. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Database Type	The type of the source database. Select PolarDB (Compatible with Oracle).
	Access Method	The access method of the source database. Select Public IP Address.
	Instance Region	The region in which the source PolarDB for PostgreSQL (Compatible with Oracle) cluster resides.
	Data Sources	Specifies whether to configure IP addresses and port numbers of multiple nodes in the source cluster. If you select Single Data Source, you must configure the Domain Name or IP Address and Port Number parameters of the primary node in the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. If you select Multiple Data Sources, you must specify the IP addresses and port numbers of multiple nodes, including the primary node, in the source PolarDB for PostgreSQL (Compatible with Oracle) cluster in the IP:Port of Data Sources field. Note If you select Multiple Data Sources and configure the IP:Port of Data Sources parameter, DTS can automatically switch to a new primary node in the PolarDB for PostgreSQL (Compatible with Oracle) cluster during primary/secondary switchover. This is applicable to scenarios such as disaster recovery. In this example, Single Data Source is selected.
	Domain Name or IP Address	The endpoint of the primary node in the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. Note You can run the ping command on your computer to obtain the IP address that is used to access the source PolarDB for PostgreSQL (Compatible with Oracle) cluster.
	Port Number	The service port number of the source database. Default value: 1521. Note In this example, the service port of the source database must be accessible over the Internet.
	IP:Port of Data Sources	The IP addresses and port numbers of multiple nodes, including the primary node, in the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. Separate multiple IP:Port with commas (,).
	Oracle Type	The architecture of the source database. If you select Non-RAC Instance, you must configure the SID parameter. If you select RAC or PDB Instance, you must configure the Service Name parameter. In this example, Non-RAC Instance is selected.
	Database Name	The name of the source database in the PolarDB for PostgreSQL (Compatible with Oracle) cluster.
	Database Account	The database account of the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.
Destination Database	Database Type	The type of the destination database. Select Oracle.
	Access Method	The access method of the destination database. Select Public IP Address.
	Instance Region	The region in which the destination Oracle database resides.
	Hostname or IP Address	The endpoint of the primary node in the destination Oracle database.
	Port Number	The service port number of the destination database. Default value: 1521.
	Oracle Type	The architecture of the destination database. If you select Non-RAC Instance, you must configure the SID parameter. If you select RAC or PDB Instance, you must configure the Service Name parameter. In this example, Non-RAC Instance is selected.
	Database Account	The account of the destination Oracle database. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.

If an IP address whitelist is configured for your self-managed database, add the CIDR blocks of DTS servers to the IP address whitelist. Then, click Test Connectivity and Proceed.
Warning
If the public CIDR blocks of DTS servers are automatically or manually added to the IP address whitelist of a database instance or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your account and password, limiting the ports that are exposed, authenticating API calls, regularly checking the IP address whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, and connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated and advanced settings.

Parameter	Description
Migration Types	To perform only full data migration, select only Full Data Migration. To ensure service continuity during data migration, select Full Data Migration and Incremental Data Migration. Note 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 have 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 You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain tables that have identical table names and the tables in the destination database cannot be deleted or renamed. 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 schemas, DTS does not migrate data records that have the same primary key values as data records in the destination database. 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 and click the icon to add the objects to the Selected Objects section. Note You can select columns, tables, or schemas as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects, such as views, triggers, or stored procedures, to the destination database.
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 to rename an object, other objects that depend on the object may fail to be migrated. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Use SQL conditions to filter data. To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information about the SQL operations that can be migrated, see the SQL operations that can be incrementally migrated section of this topic.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Set Alerts	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 will receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see Configure monitoring and alerting.
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 time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you set different retry time ranges for multiple data migration tasks that have the same source or destination database, the shortest retry time range that is set 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 your earliest opportunity after the source and destination instances are released.
The wait time before a retry when other issues occur in the source and destination databases.	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 The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Configure ETL	Specifies whether to configure 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.

In the lower part of the page, click Next: Save Task Settings and Precheck.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameters to be specified when you call the relevant API operation to configure the DTS task.
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 troubleshoot the issues based on the error message, you can run a precheck again.
- If an alert is triggered for an item during the precheck:
  If the 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.
Wait until the 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 Specifications 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 to start the data migration task. You can view the progress of the task in the task list.