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Data Transmission Service:Synchronize data from a self-managed Oracle database to a PolarDB-X 2.0 instance

Last Updated:Apr 25, 2024

This topic describes how to synchronize data from a self-managed Oracle database to a PolarDB-X 2.0 instance by using Data Transmission Service (DTS).

Prerequisites

  • A self-managed Oracle database and a PolarDB-X 2.0 instance are created. The version of the self-managed Oracle database is 19c, 18c, 12c, 11g, 10g, or 9i.

  • 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.

  • The available storage space of the PolarDB-X 2.0 instance is larger than the total size of the data in the self-managed Oracle database.

  • You are familiar with the capabilities and limits that DTS has if DTS is used to synchronize data from an Oracle database. Advanced Database & Application Migration (ADAM) is used for database evaluation. This helps you smoothly synchronize data to the cloud. 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.

Category

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 RAC database connected over Express Connect, you must specify a 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, Data Transmission Service (DTS) may fail to obtain the redo logs and archive logs, which causes the task to fail, or even data inconsistency or data loss. 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.

  • During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases. For example, if you use tools other than DTS to write data to the destination database, data loss may occur in the destination database when you use DMS to perform online DDL operations.

Billing

Synchronization typeTask configuration fee
Schema synchronization and full data synchronizationFree of charge.
Incremental data synchronizationCharged. For more information, see Billing overview.

Supported synchronization topologies

  • One-way one-to-one synchronization

  • One-way one-to-many synchronization

  • One-way many-to-one synchronization

  • One-way cascade synchronization

For more information about the synchronization topologies that are supported by DTS, see Synchronization topologies.

SQL operations that can be synchronized

Operation type

SQL statement

DML

INSERT, UPDATE, and DELETE

DDL

  • CREATE TABLE, ALTER TABLE, DROP TABLE, RENAME TABLE, and TRUNCATE TABLE

  • CREATE VIEW, ALTER VIEW, and DROP VIEW

  • CREATE PROCEDURE, ALTER PROCEDURE, and DROP PROCEDURE

  • CREATE FUNCTION, DROP FUNCTION, CREATE TRIGGER, and DROP TRIGGER

  • CREATE INDEX and DROP INDEX

Permissions required for database accounts

Database

Required permission

References

Self-managed Oracle database

Fine-grained permissions

Prepare a database account, CREATE USER, and GRANT

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

  1. Go to the Data Synchronization 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 Synchronization.

    Note
  2. 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.

  3. Click Create Task. In the Create Data Synchronization Task wizard, 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 a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.

    Source Database

    Select a DMS database instance

    Select whether to use an existing instance.

    • 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 source database. Select Oracle.

    Access Method

    The access method of the source database. In this example, Self-managed Database on ECS is selected.

    Note

    If your source database is a self-managed database, you must deploy the network environment for the database. For more information, see Preparation overview.

    Instance Region

    The region in which the source self-managed Oracle database resides.

    Instance ID

    The ID of the Elastic Compute Service (ECS) instance that hosts the source self-managed Oracle database.

    Port Number

    The service port number of the source self-managed Oracle database. Default value: 1521.

    Oracle Type

    The architecture type of the source self-managed Oracle database. In this example, RAC or PDB Instance is selected.

    • 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.

    Database Account

    The account of the source self-managed Oracle database.

    Database Password

    The password of the database account.

    Destination Database

    Select a DMS database instance

    Select whether to use an existing instance.

    • 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-X 2.0.

    Access Method

    The access method of the destination database. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the destination PolarDB-X 2.0 instance resides.

    Database Account

    The database account of the destination PolarDB-X 2.0 instance. The account must have the read and write permissions on the destination PolarDB-X 2.0 instance.

    Database Password

    The password of the database account.

  4. 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 make sure that the ECS instance can access the database. If the database is deployed on multiple ECS instances, you must manually add the CIDR blocks of DTS servers to the security group rules of each ECS instance. 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.

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

    Parameter

    Description

    Synchronization Types

    The 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 the selected objects from the source database to the destination cluster. 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

      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 synchronized 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 in the destination database has the same primary key value or unique key value as a data record in the source 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. In this case, only some columns are synchronized, or the data synchronization task fails. Proceed with caution.

    Source Objects

    Select one or more objects from the Source Objects section and click the 向右 icon to move the objects to the Selected Objects section.

    Note

    You can select columns, tables, or databases as the objects to be synchronized. If you select tables or columns as the objects to be synchronized, DTS does not synchronize other objects such as views, triggers, and stored procedures to the destination database.

    Selected Objects

    • To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the Map the name of a single object section of the "Map object names" topic.

    • To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the Map multiple object names at a time section of the "Map object names" topic.

    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 about the SQL statements that can be synchronized, see the SQL operations that can be synchronized section of this topic.

    • To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Set filter conditions.

  6. Click Next: Advanced Settings to configure advanced settings.

    Parameter

    Description

    Select the dedicated cluster used to schedule the task

    By default, DTS schedules tasks to shared clusters. You do not need to configure this parameter. You can purchase a dedicated cluster of specific specifications to run DTS data 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 this 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 specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range 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 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 this 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 Connections parameter.

    Enable Throttling for Full Data Migration

    During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can 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 for full data synchronization tasks to reduce the load on the destination database server.

    Note

    This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter.

    Enable Throttling for Incremental Data Synchronization

    Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.

    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:

    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.

  7. 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 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 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 issue. 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.

  8. Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

  9. 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 your subscription 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 billed on an hourly basis. We recommend that you select the pay-as-you-go billing method for short-term use. If you no longer require a pay-as-you-go instance, you can release the instance to reduce costs.

    Resource Group

    The resource group to which the instance belongs. 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 requirements. For more information, see Specifications of data synchronization instances.

    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 displayed only if you select the subscription billing method.Subscription

  10. Read and select the Data Transmission Service (Pay-as-you-go) Service Terms.

  11. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.