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    Data Transmission Service:Migrate data from PolarDB for PostgreSQL (Compatible with Oracle) to Kafka

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    Data Transmission Service:Migrate data from PolarDB for PostgreSQL (Compatible with Oracle) to Kafka

    Last Updated:Jan 17, 2026

    This topic describes how to use Data Transmission Service (DTS) to migrate data from a PolarDB for PostgreSQL (Compatible with Oracle) cluster to a Message Queue for Apache Kafka instance.

    Prerequisites

    • The value of the wal_level parameter is set to logical for the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. This adds the information required for logical decoding to the write-ahead log (WAL). For more information, see Set cluster parameters.

    • A destination Message Queue for Apache Kafka instance is created. The destination instance must have more available disk space than the disk space used by the source PolarDB for PostgreSQL (Compatible with Oracle) instance.

      Note

      For information about the supported database versions, see Migration solutions.

    • A topic is created in the destination Message Queue for Apache Kafka instance to receive the migrated data. For more information, see Step 1: Create a topic.

    Precautions

    Type

    Description

    Source database limits

    • Bandwidth: The source database server must have sufficient egress bandwidth. Otherwise, the data migration speed is affected.

    • Tables to be migrated must have a primary key or a UNIQUE constraint, and the fields in the constraint must be unique. Otherwise, duplicate data may occur in the destination database.

    • If you migrate objects at the table level and need to edit them, such as mapping column names, a single data migration task can migrate a maximum of 1,000 tables. If you exceed this limit, an error is reported when you submit the task. In this case, split the tables into smaller batches and configure multiple tasks, or configure a task to migrate the entire database.

    • If you perform incremental migration, for the write-ahead log (WAL):

      • Enable it.

      • For incremental migration tasks, DTS requires the source database to retain WAL logs for more than 24 hours. For tasks that include both full and incremental migration, DTS requires the source database to retain WAL logs for at least 7 days. After the full migration is complete, you can change the log retention period to more than 24 hours. If the retention period is too short, the DTS task may fail because DTS cannot obtain the required WAL logs. In extreme cases, this can lead to data inconsistency or data loss. Issues caused by a log retention period that is shorter than the DTS requirement are not covered by the DTS Service-level agreement (SLA).

    • Source database operation limits:

      • During the schema migration and full migration phases, do not perform DDL operations that change the database or table structure. Otherwise, the data migration task fails.

      • If you perform only full data migration, do not write new data to the source instance. Otherwise, data inconsistency occurs between the source and destination. To maintain real-time data consistency, select schema migration, full data migration, and incremental data migration.

      • To ensure the migration task runs properly and to prevent logical subscription interruptions caused by a primary/secondary switchover, your PolarDB for PostgreSQL (Compatible with Oracle) instance must support and have Logical Replication Slot Failover enabled. For more information, see Enable Logical Replication Slot Failover.

        Note

        If the source PolarDB for PostgreSQL (Compatible with Oracle) cluster does not support the logical replication slot failover feature (for example, when the cluster's Database Engine is Oracle Syntax Compatible 2.0), the migration instance may fail and cannot be recovered when the source database triggers an HA failover.

      • Due to the limits of logical replication in the source database, if a single piece of incremental data to be migrated exceeds 256 MB during the migration, the DTS instance may fail and cannot be recovered. You must reconfigure the DTS instance.

    • If the source database has long-running transactions and the instance includes an incremental migration task, the write-ahead log (WAL) before the transaction commit may accumulate and cannot be cleared. This can lead to insufficient disk space in the source database.

    Other limits

    • A single data migration task can migrate only one database. To migrate multiple databases, configure a data migration task for each database.

    • DTS does not support the migration of TimescaleDB extension tables or tables with cross-schema inheritance.

    • DTS does not support migrating INDEX, PARTITION, VIEW, PROCEDURE, FUNCTION, TRIGGER, and FK objects.

    • If the DTS instance performs an incremental data migration task, you must run the ALTER TABLE schema.table REPLICA IDENTITY FULL; command on the tables to be migrated in the source database before you write data to them. This applies to the following two scenarios and ensures data consistency. During the execution of this command, we recommend that you do not perform table lock operations. Otherwise, the tables may be locked. If you skip the relevant check in the precheck, DTS automatically runs this command during the instance initialization.

      • When the instance runs for the first time.

      • When the migration object granularity is Schema, and a new table is created in the schema to be migrated or a table to be migrated is rebuilt using the RENAME command.

      Note

      • In the command, replace schema and table with the schema name and table name of the data to be migrated.

      • We recommend that you perform this operation during off-peak hours.

    • DTS creates the following temporary tables in the source database to obtain DDL statements for incremental data, the schemas of incremental tables, and heartbeat information. Do not delete these temporary tables during the migration. Otherwise, the DTS task becomes abnormal. The temporary tables are automatically deleted after the DTS instance is released.

      public.dts_pg_class, public.dts_pg_attribute, public.dts_pg_type, public.dts_pg_enum, public.dts_postgres_heartbeat, public.dts_ddl_command, public.dts_args_session, and public.aliyun_dts_instance.

    • To ensure the accuracy of the displayed migration latency, DTS adds a table named dts_postgres_heartbeat to the source database.

    • During incremental data migration, DTS creates a replication slot with the prefix dts_sync_ in the source database to replicate data. Using this replication slot, DTS can obtain incremental logs from the source database within the last 15 minutes. When the data migration fails or the migration instance is released, DTS attempts to automatically clear this replication slot.

      Note

      • If you change the password of the source database account used by the task or delete the DTS IP address from the whitelist of the source database during data migration, the replication slot cannot be automatically cleared. In this case, you must manually clear the replication slot in the source database to prevent it from accumulating and occupying disk space, which can make the source database unavailable.

      • If a failover occurs in the source database, you must log on to the secondary database to manually clear the slot.

    • During data migration, if the destination Kafka instance is scaled out or scaled in, you must restart the migration instance.

    • Before you migrate data, evaluate the performance of the source and destination databases. We also recommend that you migrate data during off-peak hours. Otherwise, DTS consumes read and write resources on the source and destination databases during full data migration, which may increase the database load.

    • DTS attempts to resume failed migration tasks within seven days. Before you switch your business to the destination instance, make sure to end or release the task, or revoke the write permissions of the account that DTS uses to access the destination instance. This prevents the source data from overwriting the data in the destination instance after the task is automatically resumed.

    • If the task fails, DTS technical support will attempt to recover it within 8 hours. During the recovery process, operations such as restarting the task or adjusting its parameters may be performed.

      Note

      When parameters are adjusted, only DTS task parameters are modified. Database parameters remain unchanged.The parameters that may be modified include but are not limited to those described in Modify instance parameters.

    • When migrating partitioned tables, include both the child partitions and the parent table as synchronization objects. Otherwise, data inconsistency may occur for the partitioned table.

      Note

      The parent table of a partitioned table in PolarDB for PostgreSQL (Compatible with Oracle) does not directly store data. All data is stored in the child partitions. The sync task must include both the parent table and all its child partitions. Otherwise, data from the child partitions may be missed, which leads to data inconsistency between the source and destination.

    Billing

    Migration type

    Link configuration fees

    Data transfer cost

    Schema migration and full data migration

    Free of charge.

    You are charged for data transfer when you migrate data out of Alibaba Cloud over the public network. For more information, see Billing overview.

    Incremental data migration

    Charged. For more information, see Billing overview.

    SQL operations that support incremental migration

    Operation type

    SQL statement

    DML

    INSERT, UPDATE, DELETE

    DDL

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

    • CREATE VIEW, ALTER VIEW, DROP VIEW

    • CREATE PROCEDURE, ALTER PROCEDURE, DROP PROCEDURE

    • CREATE FUNCTION, DROP FUNCTION

    • CREATE INDEX, DROP INDEX

    Important

    • Additional information in DDL statements, such as CASCADE or RESTRICT, is not supported.

    • DDL statements in a session where the SET session_replication_role = replica command is run are not supported.

    • DDL statements that are run by calling a FUNCTION or other methods are not supported.

    • If multiple SQL statements submitted from the source database at one time contain both DML and DDL statements, the DDL statements are not migrated.

    • If multiple SQL statements submitted from the source database at one time contain DDL statements for objects that are not to be migrated, the DDL statements are not migrated.

    Permissions required for database accounts

    Database

    Required permissions

    Account creation and authorization method

    PolarDB for PostgreSQL (Compatible with Oracle) cluster

    Privileged account

    Create and manage a database account

    Procedure

    1. Go to the migration task list page of the destination region. You can use one of the following methods.

      From the DTS console

      1. Log on to the Data Transmission Service (DTS) console.

      2. In the navigation pane on the left, click Data Migration.

      3. In the upper-left corner of the page, select the region where the migration instance is located.

      From the DMS console

      Note

      The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode console and Customize the layout and style of the DMS console.

      1. Log on to the Data Management (DMS) console.

      2. In the top navigation bar, choose Data + AI > Data Transmission (DTS) > Data Migration.

      3. To the right of Data Migration Tasks, select the region where the migration instance is located.

    2. Click Create Task to go to the task configuration page.

    3. Configure the source and destination databases.

      Note

      For information about how to obtain the parameters of the destination Message Queue for Apache Kafka instance, see Configure the parameters of a Message Queue for Apache Kafka instance.

      Category

      Configuration

      Description

      N/A

      Task Name

      DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not have to be unique.

      Source Database

      Select Existing Connection

      • To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured.

        Note

        In the DMS console, this parameter is named Select a DMS database instance..

      • If you have not registered the database instance with the system, or do not need to use a registered instance, manually configure the database information below.

      Database Type

      Select PolarDB (Compatible with Oracle).

      Access Method

      Select Alibaba Cloud Instance.

      Instance Region

      Select the region where the source PolarDB for PostgreSQL (Compatible with Oracle) cluster resides.

      Replicate Data Across Alibaba Cloud Accounts

      This example migrates data within the same Alibaba Cloud account. Select No.

      Instance ID

      Select the ID of the source PolarDB for PostgreSQL (Compatible with Oracle) cluster.

      Database Name

      Enter the name of the database that contains the objects to be migrated from the source PolarDB for PostgreSQL (Compatible with Oracle) cluster.

      Database Account

      Enter the database account of the source PolarDB for PostgreSQL (Compatible with Oracle) cluster. For information about the required permissions, see Permissions required for database accounts.

      Database Password

      Enter the password that corresponds to the database account.

      Destination Database

      Select Existing Connection

      • To use a database instance that has been added to the system (created or saved), select the desired database instance from the drop-down list. The database information below will be automatically configured.

        Note

        In the DMS console, this parameter is named Select a DMS database instance..

      • If you have not registered the database instance with the system, or do not need to use a registered instance, manually configure the database information below.

      Database Type

      Select Kafka.

      Access Method

      Select Express Connect, VPN Gateway, or Smart Access Gateway.

      Note

      Here, the Message Queue for Apache Kafka instance is configured as a self-managed Kafka database for the migration instance.

      Instance Region

      Select the region where the destination Message Queue for Apache Kafka instance resides.

      Connected VPC

      Select the ID of the virtual private cloud (VPC) to which the destination Message Queue for Apache Kafka instance belongs.

      Domain Name or IP

      Enter any IP address from the Default Endpoint of the target ApsaraMQ for Kafka instance.

      Port Number

      Enter the service port of the target ApsaraMQ for Kafka instance. The default value is 9092.

      Database Account

      You do not need to fill in this parameter for this example.

      Database Password

      Kafka Version

      Select the version of the Kafka instance.

      Encryption

      Select Non-encrypted or SCRAM-SHA-256 based on your business and security requirements.

      Topic

      Select the topic to receive data from the drop-down list.

      Use Kafka Schema Registry

      Kafka Schema Registry is a metadata service layer that provides a RESTful interface for storing and retrieving Avro Schema.

      • No: Do not use Kafka Schema Registry.

      • Yes: Use Kafka Schema Registry. You must enter the URL or IP address of the Avro schema registered in Kafka Schema Registry in the URL or IP Address of Schema Registry text box.

    4. After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page.

      Note

      • Ensure that the IP address segment of the DTS service is automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.

      • If the source or destination database is a self-managed database (the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box that appears.

    5. Configure the task objects.

      1. On the Configure Objects page, configure the objects to be migrated.

        Configuration

        Description

        Migration Types

        • If you only need to perform a full migration, select both Schema Migration and Full Data Migration.

        • To perform a zero-downtime migration, select Schema Migration, Full Data Migration, and Incremental Data Migration.

        Note

        • If the Access Method of the destination Kafka instance is Alibaba Cloud Instance, Schema Migration is not supported.

        • If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.

        Processing Mode of Conflicting Tables

        • Precheck and Report Errors: Checks whether tables with the same names exist in the destination database. If no tables with the same names exist, the precheck item is passed. If tables with the same names exist, an error is reported during the precheck phase, and the data migration task does not start.

          Note

          If a table in the destination database has the same name but cannot be easily deleted or renamed, you can change the name of the table in the destination database. For more information, see Object name mapping.

        • Ignore Errors and Proceed: Skips the check for tables with the same names.

          Warning

          Selecting Ignore Errors and Proceed may cause data inconsistency and business risks. For example:

          • If the table schemas are consistent and a record in the destination database has the same primary key value as a record in the source database:

            • During full migration, DTS keeps the record in the destination cluster. The record from the source database is not migrated to the destination database.

            • During incremental migration, DTS does not keep the record in the destination cluster. The record from the source database overwrites the record in the destination database.

          • If the table schemas are inconsistent, only some columns of data may be migrated, or the migration may fail. Proceed with caution.

        Data Format in Kafka

        Select the desired data format for storage in the Kafka instance.

        • If you select Canal JSON, see Canal JSON for parameter descriptions and examples.

          Note

          Currently, only the China (Qingdao) and China (Beijing) regions support selecting Canal JSON.

        • If you select DTS Avro, you must parse the data based on the DTS Avro schema definition. For more information, see DTS Avro schema definition and DTS Avro deserialization sample code.

        • If you select Shareplex JSON, see Shareplex Json for parameter descriptions and examples.

        Kafka Data Compression Format

        Select the compression format for Kafka messages based on your requirements.

        • LZ4 (Default): Low compression ratio, high compression speed.

        • GZIP: High compression ratio, low compression speed.

          Note

          CPU usage is high.

        • Snappy: Medium compression ratio, medium compression speed.

        Policy for Shipping Data to Kafka Partitions

        Select the desired policy.

        Message acknowledgement mechanism

        Select the desired message acknowledgment mechanism.

        Topic That Stores DDL Information

        Select a topic from the drop-down list to store DDL information.

        Note

        If you do not select a topic, the DDL information is stored in the topic that receives data by default.

        Capitalization of Object Names in Destination Instance

        You can configure the case sensitivity policy for the English names of migrated objects, such as databases, tables, and columns, in the destination instance. By default, DTS default policy is selected. You can also choose to keep it consistent with the default policy of the source or destination database. For more information, see Case sensitivity of object names in the destination database.

        Source Objects

        In the Source Objects box, click the objects to migrate, and then click 向右小箭头 to move them to the Selected Objects box.

        Note

        You can select tables as the objects to be migrated.

        Selected Objects

        No extra configuration is needed for this example. You can use the mapping feature to set the topic name, number of topic partitions, and partition key for the source table in the destination Kafka instance. For more information, see Mapping information.

        Note

        • If you use the object name mapping feature, the migration of other objects that depend on this object may fail.

        • To select the SQL operations for incremental migration, right-click the migration object in the Selected Objects section, and select the desired SQL operations in the dialog box that appears.

      2. Click Next: Advanced Settings to configure advanced parameters.

        Configuration

        Description

        Dedicated Cluster for Task Scheduling

        By default, DTS schedules tasks on a shared cluster. You do not need to select one. If you want more stable tasks, you can purchase a dedicated cluster to run DTS migration tasks.

        Retry Time for Failed Connections

        After the migration task starts, if the connection to the source or destination database fails, DTS reports an error and immediately starts continuous retry attempts. The default retry duration is 720 minutes. You can also customize the retry time within a range of 10 to 1440 minutes. We recommend that you set it to more than 30 minutes. If DTS reconnects to the source and destination databases within the set time, the migration task automatically resumes. Otherwise, the task fails.

        Note

        • For multiple DTS instances that share the same source or destination, the network retry time is determined by the setting of the last created task.

        • Because you are charged for the task during the connection retry period, we recommend that you customize the retry time based on your business needs, or release the DTS instance as soon as possible after the source and destination database instances are released.

        Retry Time for Other Issues

        After the migration task starts, if other non-connectivity issues occur in the source or destination database (such as a DDL or DML execution exception), DTS reports an error and immediately starts continuous retry attempts. The default retry duration is 10 minutes. You can also customize the retry time within a range of 1 to 1440 minutes. We recommend that you set it to more than 10 minutes. If the related operations succeed within the set retry time, the migration task automatically resumes. Otherwise, the task fails.

        Important

        The value of Retry Time for Other Issues must be less than the value of Retry Time for Failed Connections.

        Enable Throttling for Full Data Migration

        During the full migration phase, DTS consumes some read and write resources of the source and destination databases, which may increase the database load. As needed, you can choose whether to set speed limits for the full migration task. You can set Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) to reduce the pressure on the destination database.

        Note

        • This configuration item is available only if you select Full Data Migration for Migration Types.

        • You can also adjust the full migration speed after the migration instance is running.

        Enable Throttling for Incremental Data Migration

        As needed, you can also choose whether to set speed limits for the incremental migration task. You can set RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) to reduce the pressure on the destination database.

        Note

        • This configuration item is available only if you select Incremental Data Migration for Migration Types.

        • You can also adjust the incremental migration speed after the migration instance is running.

        Environment Tag

        You can select an environment tag to identify the instance if needed. This is not required for this example.

        Configure ETL

        Choose whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values:

        Monitoring and Alerting

        Select whether to set alerts and receive alert notifications based on your business needs.

        • No: Does not set an alert.

        • Yes: Sets an alert. You must also set the alert threshold and alert notifications. The system sends an alert notification if the migration fails or the latency exceeds the threshold.

    6. Save the task and run a precheck.

      • To view the parameters for configuring this instance when you call the API operation, move the pointer over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the bubble.

      • If you do not need to view or have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.

      Note

      • Before the migration task starts, a precheck is performed. The task starts only after it passes the precheck.

      • If the precheck fails, click View Details next to the failed check item, fix the issue based on the prompt, and then run the precheck again.

      • If a warning is reported during the precheck:

        • For check items that cannot be ignored, click View Details next to the failed item, fix the issue based on the prompt, and then run the precheck again.

        • For check items that can be ignored and do not need to be fixed, you can click Confirm Alert Details, Ignore, OK, and Precheck Again to skip the alert item and run the precheck again. If you choose to shield an alert item, it may cause issues such as data inconsistency and pose risks to your business.

    7. Purchase the instance.

      1. When the Success Rate is 100%, click Next: Purchase Instance.

      2. On the Purchase page, select the link specification for the data migration instance. For more information, see the following table.

        Category

        Parameter

        Description

        New Instance Class

        Resource Group Settings

        Select the resource group to which the instance belongs. The default value is default resource group. For more information, see What is Resource Management?

        Instance Class

        DTS provides migration specifications with different performance levels. The link specification affects the migration speed. You can select a specification based on your business scenario. For more information, see Data migration link specifications.

      3. After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.

      4. Click Buy and Start, and in the OK dialog box that appears, click OK.

        You can view the progress of the migration instance on the Data Migration Tasks list page.

        Note

        • If the migration instance does not include an incremental migration task, it stops automatically. After the instance stops, its Status is Completed.

        • If the migration instance includes an incremental migration task, it does not stop automatically, and the incremental migration task continues to run. While the incremental migration task is running normally, the Status of the instance is Running.

    Mapping information

    1. In the Selected Objects area, hover the mouse pointer over the destination topic name at the table level.

    2. For the target topic, click Edit.

    3. In the Edit Table dialog box, you can configure the mapping information.

      Note

      • At the schema level, the dialog box is named Edit Schema and contains fewer configurable parameters. At the table level, the dialog box is named Edit Table.

      • If the migration granularity is not an entire schema, you cannot modify the Name of target Topic or Number of Partitions in the Edit Schema dialog box.

      Configuration

      Description

      Name of target Topic

      The name of the destination Topic to which the source table is migrated. By default, this is the Topic selected in the Destination Database section during the Configurations for Source and Destination Databases step.

      Important

      • If the destination database is a Message Queue for Apache Kafka instance, the specified topic name must exist in the destination Kafka instance. Otherwise, the data migration fails. If the destination database is a self-managed Kafka database and the migration instance includes a schema migration task, DTS attempts to create the topic you specify in the destination database.

      • If you modify the Name of target Topic, the data is written to the topic you specify.

      Filter Conditions

      For more information, see Set filter conditions.

      Number of Partitions

      The number of partitions for the destination topic to which data is written.

      Partition Key

      When Policy for Shipping Data to Kafka Partitions is set to Ship Data to Separate Partitions Based on Hash Values of Primary Keys, you must configure this parameter. Specify one or more columns as the Partition Key to calculate a hash value. DTS delivers different rows to each partition of the destination topic based on the calculated hash values. Otherwise, this delivery policy does not take effect during the incremental write phase.

      Note

      You can select Partition Key only in the Edit Table dialog box.

    4. Click OK.