Migrate data from a PolarDB for PostgreSQL (Compatible with Oracle) cluster to an AnalyticDB for MySQL V3.0 cluster - Data Transmission Service

You can use Data Transmission Service (DTS) to migrate data from a PolarDB for PostgreSQL (Compatible with Oracle) cluster to an AnalyticDB for MySQL V3.0 cluster.

Prerequisites

A destination AnalyticDB for MySQL V3.0 cluster has been created. For more information, see Create a cluster.
In the source PolarDB for PostgreSQL (Compatible with Oracle) cluster, the wal_level parameter is set to logical. This indicates that the information required for logical encoding is added to the write-ahead logging (WAL) logs. For more information, see Configure cluster parameters.

Precautions

Note

During schema migration, DTS does not migrate 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 update and delete operations on the source database during data migration, data inconsistency may occur.

Type	Description
Source database limits	Bandwidth requirements: The server of the source database must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. 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. If you select tables as the migration objects and need to edit them, such as mapping table or column names, you can migrate a maximum of 1,000 tables in a single migration task. If you exceed this limit, a request error is reported after you submit the task. In this case, split the tables to be migrated and configure multiple tasks to run in batches, or configure a migration task for the entire database. If you perform incremental migration, the following requirements for WALs apply: This must be enabled. For an incremental migration task, DTS requires that the WALs of the source database are retained for more than 24 hours. For a task that includes both full migration and incremental migration, DTS requires that the WALs of the source database are retained for at least 7 days. You can set the retention period of WALs to more than 24 hours after the full migration is complete. Otherwise, DTS may fail to obtain the WALs, which causes the task to fail. In extreme cases, data inconsistency or loss may occur. Issues caused by setting a WAL retention period shorter than required by DTS are not covered by the DTS Service-Level Agreement (SLA). Limits on source database operations: During schema migration and full data migration, do not perform DDL operations to change the database or table structures. 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 databases. To maintain real-time data consistency, select schema migration, full data migration, and incremental data migration. If you want to perform a primary/secondary switchover on the source PolarDB for PostgreSQL(Compatible with Oracle) cluster, the Logical Replication Slot Failover feature must be enabled. This prevents logical subscriptions from being interrupted and ensures that your data synchronization task can run as expected. For more information, see Logical replication slot failover. Due to the limits on logical subscriptions in the source database, if a single piece of data to be migrated from the source database exceeds 256 MB after an incremental change during the running of a migration instance that includes an incremental task, the migration instance may fail and cannot be recovered. You need to reconfigure the migration instance. If long-running transactions exist in the source database and the instance includes an incremental migration task, the write-ahead logs (WALs) before the long-running transactions are committed may accumulate and cannot be cleared. This can cause the disk space of the source database to become insufficient.
Other limits	A single data migration task can migrate only one database. To migrate multiple databases, you must configure a data migration task for each database. You must specify a custom primary key in the destination database or configure Primary Key Column during the Configurations for Databases, Tables, and Columns. Otherwise, data may fail to be migrated. DTS does not support migrating TimescaleDB extension tables or tables with cross-schema inheritance relationships. If the migration instance includes an incremental data migration task, you must run the `ALTER TABLE schema.table REPLICA IDENTITY FULL;` command on the table to be migrated in the source database before you write data to it in the following two scenarios. This ensures data consistency for the table migration. During the execution of this command, we recommend that you do not perform table locking operations. Otherwise, the table will be locked. If you skip the relevant check in the precheck, DTS automatically runs this command when the instance is initialized. 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 the DDL statements of incremental data, the schemas of incremental tables, and the heartbeat information. During data migration, do not delete temporary tables in the source database. Otherwise, the data migration task may fail. After the DTS instance is released, temporary tables are automatically deleted. `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 latency for incremental data migration, DTS adds a heartbeat 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. DTS can use this replication slot to obtain incremental logs from the source database within 15 minutes. Note DTS automatically deletes the replication slot after the instance is released. If you change the database password or delete the DTS IP address from the whitelist during migration, the replication slot cannot be automatically deleted. In this case, you must manually delete the replication slot from the source database to prevent it from accumulating and occupying disk space, which can make the ApsaraDB RDS for PostgreSQL instance unavailable. When a migration task is released or fails, DTS automatically clears the replication slot. If a primary/secondary failover occurs on the ApsaraDB RDS for PostgreSQL instance, you need to log on to the secondary database to manually clear the replication slot. Due to the limits of AnalyticDB for MySQL V3.0, if the disk space usage of nodes in an AnalyticDB for MySQL V3.0 cluster exceeds 80%, the DTS task becomes abnormal and latency is generated. Estimate the required space based on the objects to be migrated and make sure that the destination cluster has sufficient storage space. If the destination AnalyticDB for MySQL 3.0 cluster is being backed up when the DTS task is running, the task fails. Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS consumes read and write resources of the source and destination databases, which may increase the database load. Confirm that the migration precision for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS uses the `ROUND(COLUMN,PRECISION)` function to read values from these columns. If you do not explicitly define the precision, DTS sets the migration precision for FLOAT to 38 digits and for DOUBLE to 308 digits. DTS attempts to resume migration tasks that have failed within the last seven days. Before you switch your workloads to the destination instance, you must end or release the task, or run the `revoke` command to revoke the write permissions of the account that DTS uses to access the destination instance. This prevents data in the destination instance from being overwritten by data from the source database after the task is automatically resumed. If a DDL statement fails to be written to the destination database, the DTS task continues to run. You need to view the failed DDL statement in the task logs. For information about how to view task logs, see Query task logs. If an instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, operations such as restarting the instance and adjusting parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters of the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters. When you migrate partitioned tables, you must include the child partitions and the parent table as synchronization objects. Otherwise, data inconsistency may occur for the partitioned table. Note In PolarDB for PostgreSQL (Compatible with Oracle), the parent table of a partitioned table does not directly store data. All data is stored in the child partitions. The synchronization task must include both the parent table and all its child partitions. Otherwise, data from the child tables may be missed during synchronization, which leads to data inconsistency between the destination and the source.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	When the Access Method parameter of the destination database is set to Public IP Address, you are charged for Internet traffic. 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 schema definitions of migration objects to the destination database. Currently, DTS supports schema migration for tables.
Full data migration	DTS migrates all historical data of the migration objects from the source database to the destination database. Note Before schema migration and full data migration are complete, do not perform DDL operations on the migration objects. Otherwise, the migration may fail.
Incremental data migration	After the full data migration, DTS polls and captures redo logs from the source database and migrates the incremental data to the destination database. Incremental data migration lets you smoothly migrate data without stopping your applications.

SQL operations that can be incrementally migrated

Operation type	SQL operation
DML	INSERT, UPDATE, DELETE Note When data is written to the destination AnalyticDB for MySQL V3.0 cluster, the UPDATE statement is automatically converted to the REPLACE INTO statement. If the UPDATE statement is executed on the primary key, the UPDATE statement is converted to the DELETE and INSERT statements.

Permissions required for database accounts

Database	Required permissions	Account creation and authorization method
PolarDB for PostgreSQL (Compatible with Oracle) cluster	A privileged account.	For more information, see Create a database account.
AnalyticDB for MySQL V3.0	Read and write permissions on the destination database that contains the migration objects.	For more information, see Create a database account.

Procedure

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation 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.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data + AI > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

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.

Category	Configuration	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	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.
	Instance ID	Select the instance ID of the source PolarDB for PostgreSQL (Compatible with Oracle) cluster.
	Database Name	Enter the name of the database to which the migration objects belong in 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	The password that is used to access the database instance.
Destination Database	Database Type	Select AnalyticDB MySQL 3.0.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination AnalyticDB for MySQL V3.0 database resides.
	Instance ID	Select the ID of the destination AnalyticDB for MySQL V3.0 cluster.
	Database Account	Enter the account of the destination AnalyticDB for MySQL V3.0 database. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.

In the lower part of the page, click Test Connectivity and Proceed.
Note
- Make sure that the CIDR blocks of DTS servers can be 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 and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be migrated.

On the Configure Objects page, configure the objects that you want to migrate.

Configuration	Description
Migration Types	Select the migration types based on your business requirements. The migration types must be supported by the database engine. 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 Schema Migration, make sure a database and a table are created in the destination database to receive data and the object name mapping feature is enabled in Selected Objects. If you do not select Incremental Data Migration, we recommend that you do not write data to the source database during data migration. This ensures data consistency between the source and destination databases.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that 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 tables with identical 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, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates 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, only specific columns are migrated or the data migration task fails. Proceed with caution.
DDL and DML Operations to Be Synchronized	Select the DDL or DML operations to migrate at the instance level. For information about supported operations, see SQL operations that can be incrementally migrated. Note To select SQL operations for incremental migration at the table level, right-click the migration object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate.
Merge Tables	Yes: If you select this value, DTS adds the `__dts_data_source` column to each table to record data sources. For more information, see Enable the multi-table merging feature. No: This is the default value. Note If you set this parameter to Yes, all of the selected source tables in the task are merged into a destination table. If you do not need to merge specific source tables, you can create a separate data migration task for these tables. Warning We recommend that you do not perform DDL operations to change the schemas of source databases or tables. Otherwise, data inconsistency may occur or the data migration task may fail.
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 make sure that the capitalization of object names is consistent with that of 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. Click the icon to add the objects to the Selected Objects section. Important If you select Incremental Data Migration for Migration Types, you can select only a single data table. If you do not select Incremental Data Migration for the Migration Types parameter, the objects to be migrated can be databases, tables, and columns. If you select a database as the object to be migrated, DTS migrates data based on the following default rules: If the table to be migrated in the source database has a primary key, such as a single-column primary key or a composite primary key, the primary key columns are specified as the distribution keys. If the table to be migrated in the source database does not have a primary key, an auto-increment primary key column is automatically generated in the destination table. This may cause data inconsistency between the source and destination databases.
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, other objects that depend on the renamed object may fail to be migrated. To set WHERE conditions to filter data, right-click a table to be migrated in the Selected Objects section. In the dialog box that appears, set the filter conditions. For more information, see Set filter conditions. To select SQL operations for migration at the database or table level, right-click the object to be migrated in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration tasks, purchase a dedicated cluster. 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 1,440. 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.
Retry Time for Other Issues	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 Retry Time for Other Issues 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 if 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 if you select Incremental Data Migration for the Migration Types parameter.
Environment Tag	You can select an environment tag to identify the instance. This is not required.
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. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the Configure monitoring and alerting when you create a DTS task section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure the data verification task.
For more information about how to use the data verification feature, see Configure a data verification task.
Optional: After you complete the previous configurations, click Next: Configure Database and Table Fields. Then, configure the Type, Primary Key Column, Distribution Key, and partition key parameters for the tables to be migrated to the destination database. Partition key parameters include Partition Key, Partitioning Rules, and Partition Lifecycle.
Note
- This step is available only if you select Schema Migration for Migration Types. To make modifications, select All for Definition Status.
- In the Primary Key Column field, you can select multiple columns to form a composite primary key. In this case, you must select one or more Primary Key Column as Distribution Key and Partition Key. For more information, see CREATE TABLE.

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 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 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 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.

Purchase the instance.

Wait until 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 Instance classes 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. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.