Synchronize data from Oracle to PolarDB for PostgreSQL (Compatible with Oracle) - Data Transmission Service

PolarDB for PostgreSQL (Compatible with Oracle) clusters support configuration upgrade and downgrade within minutes, fault recovery within seconds, and data backup and disaster recovery with global data consistency. This topic describes how to synchronize data from a self-managed Oracle database to a PolarDB for PostgreSQL (Compatible with Oracle) cluster by using Data Transmission Service (DTS).

Prerequisites

The destination PolarDB for PostgreSQL (Compatible with Oracle) cluster is created. The available storage space of this cluster is larger than the total size of the data in the source self-managed Oracle database.
Note
- For more information, see Create a PolarDB for PostgreSQL (Compatible with Oracle) cluster.
- For more information about the supported versions of the source database and the destination cluster, see Overview of data synchronization scenarios.
A database is created in the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster to receive data. For more information, see Database management.
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 of DTS when it is used to synchronize data from an Oracle database. Advanced Database & Application Migration (ADAM) is used to evaluate the feasibility and costs of database synchronization. This helps you smoothly synchronize data from Oracle to PolarDB for PostgreSQL (Compatible with Oracle). For more information, see Prepare an Oracle database and Overview.

Limits

Note

During schema synchronization, DTS synchronizes foreign keys from the source database to the destination database.
During full data synchronization and incremental data synchronization, 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 synchronization, data inconsistency may occur.

Limit type	Description
Limits on the source database	Requirements for the objects to be synchronized: The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records. If the version of your Oracle database is 12c or later, the names of the tables to be synchronized cannot exceed 30 bytes in length. If you select tables as the objects to be synchronized and you want to edit the tables in the destination database, such as renaming tables or columns, you can synchronize up to 1,000 tables in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database. 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 data synchronization task. If the self-managed Oracle database is an Oracle RAC database, you can use only a VIP rather than a Single Client Access Name (SCAN) IP address when you configure the data synchronization task. After you specify the VIP, node failover of the Oracle RAC database is not supported. The redo logging and archive logging features must be enabled. Note If you perform only incremental data synchronization, the redo logs and archive logs of the source database must be stored for more than 24 hours. If you perform both full data synchronization and incremental data synchronization, the redo logs and archive logs of the source database must be stored for at least seven days. Otherwise, DTS may fail to obtain the redo logs and archive logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After the full data synchronization is complete, you can set the retention period to more than 24 hours. 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. If you perform a primary/secondary switchover on the source database when the data synchronization task is running, the task fails. The data synchronization task fails if the source database contains an empty string of the VARCHAR2 type and the corresponding column in the destination database has a NOT NULL constraint. Empty strings of the VARCHAR2 type are processed as null values in Oracle databases. During data synchronization, do not update LONGTEXT fields. Otherwise, the data synchronization task fails.
Other limits	Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During initial full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After initial full data synchronization is complete, the tablespace of the destination database is larger than that of the source database. DTS calculates the synchronization latency based on the timestamp of the latest synchronized data in the destination database and the current timestamp in the source database. If no DML operation is performed on the source database for an extended period of time, the synchronization latency may be inaccurate. If the synchronization latency is too high, you can perform a DML operation on the source database to update the latency. Note If you select an entire database as the object to be synchronized, you can create a heartbeat table. The heartbeat table is updated or receives data every second. The destination PolarDB for PostgreSQL (Compatible with Oracle) cluster generates unique indexes like `pg_oid_1498503_index` to correspond to ROWID of the source 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 synchronized contains the terminator, DTS does not write the terminator to the destination database. This causes data inconsistency between the source and destination databases. After the CHECK constraints in the source self-managed Oracle database are synchronized 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 synchronization feature of DTS. Otherwise, the data synchronization task may fail due to incompatible data types. The time zones of the source and destination databases must be the same. DTS allows you to synchronize objects of the custom type to the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. The built-in objects that are automatically generated by the source Oracle database are not synchronized. Note The PolarDB for PostgreSQL (Compatible with Oracle) cluster supports the built-in objects in the Oracle database. You do not need to synchronize these objects. Data inconsistency between the source and destination databases may occur if data from other sources is written to the destination database during data synchronization. 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

Synchronization type	Task configuration fee
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

SQL operations that can be synchronized

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

Permissions required for database accounts

Database type	Required permissions	References
Self-managed Oracle database	Fine-grained permissions	Prepare a database account, CREATE USER, and GRANT
PolarDB for PostgreSQL (Compatible with Oracle) cluster	Permissions of the schema owner	Create a database account and Database management. Note We recommend that you create a privileged account.

Important

If you synchronize 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 Synchronization Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click Data + AI.
3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
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 Synchronization Tasks page of the new DTS console.
On the right side of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Note
If you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.

Click Create Task. On the Create Task page, configure the source and destination databases. The following table describes the parameters.

Section	Parameter	Description
N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify an informative name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information.
	Database Type	The type of the source database. Select Oracle.
	Access Method	Select the access method based on the deployment location of the source database. In this example, Self-managed Database on ECS is selected. Note If you select other access methods, 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 where the source Oracle database resides.
	ECS Instance ID	The ID of the ECS instance on which the source Oracle database is deployed.
	Port Number	The service port number of the source self-managed Oracle database. Default value: 1521.
	Oracle Type	The architecture of the source Oracle database. If you select Non-RAC Instance, you must specify the SID parameter. If you select RAC or PDB Instance, you must specify the Service Name parameter. In this example, RAC or PDB Instance is selected and Service Name is specified.
	Database Account	The account of the source self-managed 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 that is used to access the database instance.
Destination Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the destination database. Select PolarDB (Compatible with Oracle).
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region where the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster resides.
	Instance ID	The ID of the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster.
	Database Name	The name of the database created in the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster to receive the objects to be synchronized.
	Database Account	The database account of the destination PolarDB for PostgreSQL (Compatible with Oracle) cluster. For more 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 that is used to access the database instance.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must ensure that the ECS instance can access the database. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database. For more information, see Add the CIDR blocks of DTS servers.
Warning
If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize 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 ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

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

Parameter	Description
Synchronization Types	By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of selected objects from the source instance to the destination instance. The historical data is the basis for subsequent incremental synchronization.
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 synchronization task cannot be started. Note You can use the object name mapping feature to rename the tables that are synchronized to the destination database. You can use this feature if the source and destination databases contain 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 potential risks. If the source and destination databases have the same schemas, and a data record has the same primary key value as an existing data record in the destination database: During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. During incremental data synchronization, DTS synchronizes 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, data may fail to be initialized, only some columns are synchronized, or the data synchronization task fails. Operate with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
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 databases, tables, or columns as the objects to be synchronized.
Selected Objects	If the destination database account is not a privileged account or the name of the database to be synchronized does not comply with the naming conventions of PolarDB for MySQL, you must perform the following operations: Right-click the schema of the object to be synchronized in the Selected Objects section. In the Edit Schema dialog box, set the Schema Name parameter to the name of the destination database that is used to receive data in the PolarDB for MySQL cluster. For more information, see Map object names. Note 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 synchronize. For more information, see the SQL operations that can be synchronized section of this topic. To filter data, right-click the table that you want to synchronize in the Selected Objects section. In the dialog box that appears, set filter conditions. For more information, see Specify filter conditions. If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be synchronized.

Click Next: Advanced Settings to configure advanced settings.

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

Advanced Settings

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules tasks to shared clusters. You do not need to configure this parameter. You can purchase a dedicated cluster of specified specifications to run DTS synchronization 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 synchronization 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 synchronization task. Otherwise, the data synchronization task fails. Note If you set different retry time ranges for multiple DTS 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.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the 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 time range, DTS resumes the data synchronization task. Otherwise, the data synchronization 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 Connection parameter.
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 configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and BPS of Full Data Migration parameters for full data synchronization tasks to reduce the pressure on the destination database. Note This parameter can be configured only if Full Data Synchronization is selected as Synchronization Types.
Enable Throttling for Incremental Data Synchronization	You can configure the RPS of Incremental Data Migration and BPS of Incremental Data Migration parameters for incremental data synchronization tasks to reduce the pressure on the destination database.
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 of the data that is written to the destination database. 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 synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert contacts. For more information, see Configure monitoring and alerting when you create a DTS task.

Click Next: Save Task Settings and Precheck in the lower part of the page.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.
Note
- Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization 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 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 an 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 Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for the instance when you create an instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is charged on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go instance, you can release the pay-as-you-go instance to reduce costs.
	Resource Group	The resource group on which the instance is run. Default value: default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business scenario. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

Read and select the check box to agree to the Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the dialog box that appears, click OK.
You can view the progress of the task in the task list.