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

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

Prerequisites

The source Oracle database and the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster are created.
Note
- For more information about how to create a PolarDB for PostgreSQL (Compatible with Oracle) cluster, see Create a PolarDB for Oracle cluster.
- For more information about supported database versions, see Overview of data migration scenarios.
The self-managed Oracle database is running in ARCHIVELOG mode. Archived log files are accessible, and an appropriate retention period is set for archived log files. For more information, see Managing Archived Redo Log Files.
The supplemental logging feature is enabled for the self-managed Oracle database, and the SUPPLEMENTAL_LOG_DATA_PK and SUPPLEMENTAL_LOG_DATA_UI parameters are set to Yes. For more information, see Supplemental Logging.
You are familiar with the capabilities and limits that DTS has if DTS is used to migrate data from an Oracle database. Advanced Database & Application Migration (ADAM) is used for database evaluation. This helps you smoothly migrate data to the cloud. For more information, see Prepare an Oracle database and Overview.

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	Bandwidth requirements: The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. If the source database is an Oracle Real Application Cluster (RAC) database connected over Express Connect, you must specify a virtual IP address (VIP) for the database when you configure the source database. If the source database is an Oracle RAC database connected over Express Connect, VPN Gateway, Smart Access Gateway, Database Gateway, or Cloud Enterprise Network (CEN), you can use a single VIP rather than a Single Client Access Name (SCAN) IP address when you configure the source database. After you specify the VIP, node failover is not supported for the Oracle RAC database. If a field in the source Oracle database contains an empty string of the VARCHAR2 type, which is evaluated as null in the Oracle database, and the corresponding field in the destination database has a NOT NULL constraint, the migration task fails. Requirements for the objects to be migrated: 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. Note You can also use the ROWID values as the primary key for an Oracle table without a primary key or UNIQUE constraint. If the version of your Oracle database is 12c or later, the names of the tables to be migrated cannot exceed 30 bytes in length. If you select tables as the objects to be migrated and you need to modify the tables in the destination database, such as renaming tables or columns, 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 in batches, or configure a task to migrate the entire database. To perform incremental migration, you must make sure that the following requirements are met: The redo logging and archive logging must be enabled. If you perform only incremental data migration, the redo logs and archive logs of the source database must be stored for more than 24 hours. If you perform both full data migration and incremental data migration, the redo logs and archive logs of the source database must be stored for at least seven days. After full data migration is complete, you can set the retention period to more than 24 hours. Otherwise, Data Transmission Service (DTS) may fail to obtain the redo logs and archive logs and the task may fail. In extreme cases, data inconsistency or loss may occur. Make sure that you set the retention period of redo logs and archive logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. Limits on operations to be performed on the source database: During schema migration and 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 may occur between the source and destination databases. To ensure data consistency, we recommend that you select schema migration, full data migration, and incremental data migration as the migration types. During data migration, do not update LONGTEXT fields. Otherwise, the data migration task fails.
Other limits	Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses read and write resources of the source and destination databases. This may increase the loads of the database servers. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination cluster. After full data migration is complete, the size of used tablespace of the destination cluster is larger than that of the source database. DTS attempts to resume the data migration task 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 a failed task is resumed. The destination PolarDB for PostgreSQL (Compatible with Oracle) cluster generates unique indexes like `pg_oid_1498503_index` to correspond to ROWID of the self-managed Oracle database. Therefore, the indexes of the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster is more than that of the source self-managed Oracle database. The destination PolarDB for PostgreSQL (Compatible with Oracle) cluster does not support the string terminator ('\0'). If the data to be migrated contains the terminator, DTS does not write the terminator to the destination database. This causes data inconsistency between the source and destination databases. When CHECK constraints created in the source Oracle database are migrated to the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster, the CHECK constraints are converted to NOT NULL constraints. Make sure that the character sets of the source and destination databases are compatible. Otherwise, data inconsistency may occur or the migration task may fail. We recommend that you use the schema migration feature of DTS. Otherwise, the migration task may fail due to incompatible data types. The time zones of the source and destination databases must be the same. Objects of the custom types can be migrated to the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. However, the objects that are automatically generated by the source Oracle database (known as built-in objects) cannot be migrated. Note PolarDB for PostgreSQL (Compatible with Oracle) clusters support the built-in objects in Oracle databases. You do not need to manually migrate data. DTS does not check the validity of metadata such as sequences. You must manually check the validity of metadata. After your workloads are switched to the destination database, newly written sequences do not increment from the maximum value of the sequences in the source database. Therefore, you must query the maximum value of the sequences in the source database before you switch your workloads to the destination database. Then, you must specify the queried maximum value as the starting value of the sequences in the destination database. You can execute the following statements to query the maximum value of the sequences in the source database: `DECLARE CURSOR cur_data IS SELECT SEQUENCE_NAME, LAST_NUMBER FROM user_sequences; v_column1_value varchar(1000); v_column2_value number(20); BEGIN OPEN cur_data; LOOP FETCH cur_data INTO v_column1_value, v_column2_value; EXIT WHEN cur_data%NOTFOUND; DBMS_OUTPUT.PUT_LINE('select setval(''' \|\| lower(v_column1_value) \|\| ''', ' \|\| v_column2_value \|\| ');'); END LOOP; CLOSE cur_data; END; /` Note The returned SQL statements contain all sequences in the source database. You can perform operations in the destination database based on your business requirements.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and 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
Schema migration	DTS migrates the schemas of the required objects to the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. DTS supports schema migration for the following object types: table, view, synonym, trigger, stored procedure, stored function, package, and user-defined type. Note In this scenario, DTS does not support schema migration for triggers. We recommend that you delete the triggers of the source database to prevent data inconsistency caused by triggers. For more information, see Configure a data synchronization task for a source database that contains a trigger.
Full data migration	DTS migrates all existing data of objects from the self-managed Oracle database to the PolarDB for PostgreSQL (Compatible with Oracle) cluster. Note During schema migration and full data migration, do not perform DDL operations on the objects to be migrated. Otherwise, the objects may fail to be migrated.
Incremental data migration	After full data migration is complete, DTS polls and retrieves redo log files from the self-managed Oracle database. Then, DTS migrates incremental data from the self-managed Oracle database to the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications during data migration.

SQL operations that can be incrementally migrated

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	CREATE TABLE Note If a CREATE TABLE statement contains partitioning clauses, subpartitioning clauses, or functions, DTS does not migrate the statement. In addition, DTS does not migrate the CREATE TABLE AS SELECT statements. ALTER TABLE, including ADD COLUMN, ADD INDEX, DROP COLUMN, DROP INDEX, MODIFY COLUMN, and RENAME COLUMN DROP TABLE RENAME TABLE, TRUNCATE TABLE, and CREATE INDEX

Before you begin

Log on to the self-managed Oracle database, create an account that you want to use to collect data, and then grant permissions to the account.

Note

If you have created an account that is granted the permissions described in the following table, you can skip this step.

Database	Schema migration	Full data migration	Incremental data migration
Self-managed Oracle database	Permissions of the schema owner	Permissions of the schema owner	Fine-grained permissions
PolarDB for PostgreSQL (Compatible with Oracle) cluster	Permissions of the schema owner

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

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

Important

If you need to migrate incremental data from an Oracle database, you must enable archive logging and supplemental logging for the Oracle database to obtain incremental data. For more information, see the Configure an Oracle database section of the "Prepare an Oracle database" topic.

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 Data Migration Task wizard, configure the source and destination databases. The following table describes the parameters.

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 Oracle.
	Access Method	The access method of the source database. In this example, Public IP Address is selected. Note If you select another access method, you must set up the environment that is required for the self-managed Oracle database. For more information, see Preparation overview.
	Instance Region	The region in which the source self-managed Oracle database resides.
	Hostname or IP address	The endpoint that is used to connect to the source self-managed Oracle database.
	Port Number	The service port number of the source self-managed Oracle database. Default value: 1521. Note In this example, the service port of the self-managed Oracle database must be accessible over the Internet.
	Oracle Type	The architecture of the source self-managed Oracle 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 source self-managed Oracle database. For information about the permissions that are required for the account, see the Before you begin section of this topic.
	Database Password	The password of the database account.
Destination Database	Database Type	The type of the destination database. Select PolarDB (Compatible with Oracle).
	Access Method	The access method of the destination database. Select Public IP Address.
	Instance Region	The region in which the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster is deployed.
	Data Sources	Single Data Source: If you select this option, you must configure the Domain Name or IP Address and Port Number parameters of the primary node in the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. Multiple Data Sources: If you select this option, you must specify the IP addresses and port numbers of multiple nodes, including the primary node, in the destination 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 suitable for 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 destination 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 destination PolarDB for PostgreSQL (Compatible with Oracle) cluster.
	Port Number	The service port number of the destination database. Default value: 1521.
	IP:Port of Data Sources	The IP addresses and port numbers of multiple nodes, including the primary node, in the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. Separate multiple IP:Port with commas (,).
	Database Name	The name of the database in the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster to which you want to migrate data.
	Database Account	The database account of the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. For information about the permissions that are required for the account, see the Before you begin 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 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 username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or security group rules and forbidding unauthorized CIDR blocks, or connecting the database instance to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure the objects to be migrated and advanced settings. The following table describes the parameters.

Parameter	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 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.
Add a hidden primary key for a table without a primary key/a table without a unique key	If the objects to be migrated contain a table without a primary key or a unique key, you must set this parameter to Yes. DTS uses the ROWID column in the Oracle database as the hidden primary key (non-null unique key) of the destination table. This prevents duplicate data in the destination database. Note You can configure this parameter only if you select Schema Migration, Full Data Migration, and Incremental Data Migration for the Migration Types parameter.
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 identical table 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, DTS does not migrate data records that have the same primary keys 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.
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 Set filter conditions. To incrementally migrate 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 incrementally migrate. For more information, see the SQL operations that can be incrementally migrated section of this topic.

Click Next: Advanced Settings to configure advanced settings.

Data Verification Settings
For more information about how to use the data verification feature, see Configure data verification.

Advanced Settings

Parameter	Description
Select the dedicated cluster used to schedule the task	By default, DTS schedules the task to a shared cluster. You do not need to configure this parameter. You can purchase a dedicated cluster of the specified specifications to run data migration tasks. 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 1440. 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.
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.
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 when 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 when you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
Actual Write Code	The encoding format in which data is written to the destination database. You can select an encoding format based on your business requirements.
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. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see the Configure monitoring and alerting for a new DTS task section of the "Configure monitoring and alerting" topic.

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 API Call to view the parameter settings of the API operation that is called to configure the instance.
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 causes, run a precheck again.
- If an alert is generated for an item during the precheck, perform the following operations based on the scenario:
  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 on the Task Management page of the data migration task.

What to do next

If the objects to be migrated contain a table without a primary key or a unique key and you set the Add a hidden primary key for a table without a primary key/a table without a unique key parameter to Yes, you must manually delete the hidden primary key that is added by DTS after you switch your business to the destination database and before you terminate or release the DTS instance. To do this, perform the following operation: On the Basic Information tab of the Full Data Migration or Incremental Write module, click Delete Invisible Primary Key in the Actions column.

Important

After the hidden primary key is deleted, make sure that the data in the source and destination databases is the same.