How to migrate data between ApsaraDB RDS for PostgreSQL instances - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to perform schema migration, full data migration, and incremental data migration between ApsaraDB RDS for PostgreSQL instances. You can combine these migration types to migrate your database without service interruptions.

Prerequisites

The source and destination ApsaraDB RDS for PostgreSQL instances must be created. For more information, see Create an ApsaraDB RDS for PostgreSQL instance.
Note
- For information about the supported versions of the source and destination databases, see Overview of data migration scenarios.
- To ensure compatibility, the version of the destination database must be the same as or later than the version of the source database. If you migrate data from a later version to an earlier version, database compatibility issues may occur.
The available disk space of the destination ApsaraDB RDS for PostgreSQL instance must be larger than the storage space occupied by the source ApsaraDB RDS for PostgreSQL instance.

Precautions

Type	Description
Source database limits	The tables to migrate must have a primary key or a UNIQUE constraint, and the fields must be unique. Otherwise, duplicate data may appear in the destination database. Note If the destination table that receives data is not created by DTS (the Schema Migration option for Migration Types is cleared), ensure that the destination table has the same primary key or non-null UNIQUE constraint as the source table. Otherwise, duplicate data may appear in the destination database. The name of the database to migrate cannot contain a hyphen (-), such as dts-testdata. If you migrate objects at the table level and need to edit them, such as using column name mapping, a single data migration task supports 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 multiple migration tasks or configure a task to migrate the entire database. DTS does not support the migration of temporary tables, internal triggers, or some functions (C-language functions and internal functions for PROCEDURE and FUNCTION) from the source database. DTS supports the migration of some custom data types (COMPOSITE, ENUM, or RANGE) and constraints such as primary keys, foreign keys, UNIQUE constraints, and CHECK constraints. For incremental migration, Write-Ahead Logging (WAL) has the following requirements: WAL must be enabled. Set the wal_level parameter to logical. For an incremental migration task, DTS requires that WAL logs in the source database are retained for more than 24 hours. For a task that includes both full migration and incremental migration, DTS requires that WAL logs are retained for at least 7 days. You can change the log retention period to more than 24 hours after the full migration is complete. If the task fails because DTS cannot obtain WAL logs, or in extreme cases, if data inconsistency or loss occurs, it is not covered by the DTS Service-Level Agreement (SLA). This is because the WAL log retention period you set is shorter than the period required by DTS. Source database operation limits: During schema migration and full data migration, do not perform DDL operations to change the schema of the database or tables. Otherwise, the data migration task fails. If you perform only full data migration, do not write new data to the source database. 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. Due to the limits of logical replication in the source database, if a single piece of data to be migrated exceeds 256 MB after an incremental change, the migration instance may fail and cannot be recovered. You must reconfigure the migration instance. If the source database has long-running transactions and the instance includes an incremental migration task, Write-Ahead Logging (WAL) data before the transaction commits may not be cleared. This can cause WAL data to accumulate and lead to insufficient disk space in the source database. If you perform a major version upgrade on the source database while the migration instance is running, the instance fails and cannot be recovered. You must reconfigure the migration instance.
Other limits	To ensure the migration task runs as expected and to prevent logical replication from being interrupted by a primary/secondary failover, your RDS for PostgreSQL instance must support and enable Logical Replication Slot Failover. For more information about how to enable this feature, see Logical Replication Slot Failover. A single data migration task can migrate only one database. To migrate multiple databases, configure a separate data migration task for each database. DTS does not support the migration of TimescaleDB extension tables or tables with cross-schema inheritance. If a table to be migrated contains a field of the SERIAL type, the source database automatically creates a Sequence for that field. Therefore, when you configure Source Objects, if you select Schema Migration for Migration Types, select Sequence or migrate the entire schema. Otherwise, the migration instance may fail. If the migration instance includes 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 writing data to them. This ensures data consistency. Do not lock the tables when you run this command. Otherwise, a deadlock may occur. If you skip the relevant check during the precheck, DTS automatically runs this command during instance initialization. This applies in the following scenarios: When the instance runs for the first time. When the migration object granularity is set to Schema, and a new table is created in the schema or an existing table is rebuilt using the RENAME command. Note In the command, replace `schema` and `table` with the actual schema name and table name. Run this command during off-peak hours. DTS validates data content but does not support the validation of metadata such as Sequences. You must validate this metadata yourself. After you switch your workloads to the destination instance, new Sequences do not increment from the maximum value of the source Sequence. You must update the Sequence value in the destination database before the switch. For more information, see Update the Sequence value in the destination database. DTS creates the following temporary tables in the source database to obtain DDL statements for incremental data, the structure of incremental tables, and heartbeat information. Do not delete these temporary tables during 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`. If a task includes full or incremental migration and the tables to be migrated contain foreign keys, triggers, or event triggers, DTS temporarily sets the session_replication_role parameter to replica at the session level. This happens if the destination database account is a privileged account or has superuser permissions. If the account does not have these permissions, you must manually set the parameter to replica in the destination database. During this period, if cascade update or delete operations occur in the source database, data inconsistency may occur. After the DTS migration task is released, you can change the session_replication_role parameter back to origin. 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 uses this replication slot to 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 clean up 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 during data migration, the replication slot cannot be automatically cleaned up. In this case, you must manually clean up the replication slot in the source database. This prevents it from accumulating and consuming disk space, which could make the source database unavailable. If a primary/secondary failover occurs in the source database, you must log on to the secondary database to perform the cleanup. Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you perform data migration during off-peak hours. Otherwise, the full data migration may consume read and write resources on both databases, which can increase the database workload. Full data migration involves concurrent INSERT operations, which can cause table fragmentation in the destination database. As a result, the table storage space in the destination database will be larger than in the source database after the full migration is complete. Confirm whether the migration precision for columns of the FLOAT or DOUBLE data type meets your business requirements. DTS reads the values of these columns using `ROUND(COLUMN,PRECISION)`. If the precision is not explicitly defined, DTS uses a precision of 38 for FLOAT and 308 for DOUBLE. DTS attempts to resume failed migration tasks within seven days. Therefore, before you switch your workloads to the destination instance, you must end or release the task. You can also run the `revoke` command to revoke the write permissions of the database account that DTS uses to access the destination instance. This prevents the source data from overwriting the data in the destination instance if the task is automatically resumed. 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 or adjusting its parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters in the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters.
Special cases	If the source instance is an RDS for PostgreSQL instance, do not change its endpoint or zone during migration. Otherwise, the migration fails.

Migration types

Schema migration
DTS migrates the schemas of the selected objects from the source database to the destination database.
Full data migration
DTS migrates the historical data of required objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications during data migration.

Supported objects

SCHEMA, TABLE
Note
This includes PRIMARY KEY, UNIQUE KEY, FOREIGN KEY, DATATYPE (built-in data types), and DEFAULT CONSTRAINT.
VIEW, PROCEDURE (PostgreSQL 11 or later), FUNCTION, RULE, SEQUENCE, EXTENSION, TRIGGER, AGGREGATE, INDEX, OPERATOR, DOMAIN

SQL operations that support incremental migration

Operation type	SQL operation
DML	`INSERT`, `UPDATE`, `DELETE`
DDL	DDL operations can be migrated only in data migration tasks that are created after . Important For data migration tasks created before May 12, 2023 (Singapore), you must create a trigger and a function in the source database to capture DDL information before you configure the task. For more information, see Use triggers and functions to implement incremental DDL migration for PostgreSQL databases. Data of the `BIT` type is not supported during incremental data migration. The following DDL statements are supported in migration tasks. The source database account must be a privileged account, and the minor engine version of the ApsaraDB RDS for PostgreSQL instance must be 20210228 or later. For information about how to update the minor engine version, see Update the minor engine version. `CREATE TABLE`, `DROP TABLE` `ALTER TABLE` (including `RENAME TABLE`, `ADD COLUMN`, `ADD COLUMN DEFAULT`, `ALTER COLUMN TYPE`, `DROP COLUMN`, `ADD CONSTRAINT`, `ADD CONSTRAINT CHECK`, and `ALTER COLUMN DROP DEFAULT`) `TRUNCATE TABLE` (The source PostgreSQL database must be PostgreSQL 11 or later.) `CREATE INDEX ON TABLE` Important Additional information in DDL statements, such as `CASCADE` or `RESTRICT`, is not migrated. DDL statements from a session where the `SET session_replication_role = replica` command is executed are not supported. DDL statements that are executed by calling a `FUNCTION` are not supported. If multiple SQL statements submitted from the source database in a single transaction contain both DML and DDL, the DDL statements are not migrated. If multiple SQL statements submitted from the source database in a single transaction contain DDL for objects that are not being migrated, the DDL statements are not migrated. DDL operations executed directly within a plugin through the Server Programming Interface (SPI) are not supported.

Permissions required for database accounts

Database	Schema migration	Full migration	Incremental migration
Source ApsaraDB RDS for PostgreSQL instance	The USAGE permission on the pg_catalog schema.	The SELECT permission on the objects to be migrated.	A privileged account that is the owner of the selected database. Note If the source instance is an ApsaraDB RDS for PostgreSQL 9.4 instance and you need to migrate only DML operations, the account only needs the REPLICATION permission.
Destination ApsaraDB RDS for PostgreSQL instance	The CREATE and USAGE permissions on the objects to be migrated.	The owner permission on the schema.

For information about how to create and grant permissions to an ApsaraDB RDS for PostgreSQL database account, see Create an account and Create a database.

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	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select PostgreSQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the source ApsaraDB RDS for PostgreSQL instance resides.
	Instance ID	Select the ID of the source ApsaraDB RDS for PostgreSQL instance.
	Database Name	Enter the name of the database that contains the objects to be migrated from the source ApsaraDB RDS for PostgreSQL instance.
	Database Account	Enter the database account of the source ApsaraDB RDS for PostgreSQL instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the source database. You can configure this parameter based on your business requirements. In this example, Non-encrypted is selected. If you want to establish an SSL-encrypted connection to the source database, perform the following steps: Select SSL-encrypted, upload CA Certificate, Client Certificate, and Private Key of Client Certificate as needed, and then specify Private Key Password of Client Certificate. Note If you set Encryption to SSL-encrypted for a self-managed PostgreSQL database, you must upload CA Certificate. If you want to use the client certificate, you must upload Client Certificate and Private Key of Client Certificate and specify Private Key Password of Client Certificate. For information about how to configure SSL encryption for an ApsaraDB RDS for PostgreSQL instance, see SSL encryption.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select PostgreSQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the destination ApsaraDB RDS for PostgreSQL instance resides.
	Instance ID	Select the ID of the destination ApsaraDB RDS for PostgreSQL instance.
	Database Name	Enter the name of the database to which objects are migrated in the destination ApsaraDB RDS for PostgreSQL instance.
	Database Account	Enter the database account of the destination ApsaraDB RDS for PostgreSQL instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the source database. You can configure this parameter based on your business requirements. In this example, Non-encrypted is selected. If you want to establish an SSL-encrypted connection to the source database, perform the following steps: Select SSL-encrypted, upload CA Certificate, Client Certificate, and Private Key of Client Certificate as needed, and then specify Private Key Password of Client Certificate. Note If you set Encryption to SSL-encrypted for a self-managed PostgreSQL database, you must upload CA Certificate. If you want to use the client certificate, you must upload Client Certificate and Private Key of Client Certificate and specify Private Key Password of Client Certificate. For information about how to configure SSL encryption for an ApsaraDB RDS for PostgreSQL instance, see SSL encryption.

Click Test Connectivity and Proceed in the lower part of the page.
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	To perform only full migration, select Schema Migration and Full Data Migration. To migrate data without service downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you select Schema Migration, DTS migrates the schema of the tables to be migrated from the source database to the destination database. The schema includes foreign keys. 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 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.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select objects to migrate at the schema or table level. If you select tables as the migration objects, other objects such as views, triggers, and stored procedures are not migrated to the destination database. If a table to be migrated contains a SERIAL field, and you select Schema Migration for Migration Types, we recommend that you also select Sequence or migrate the entire schema.
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 a WHERE clause to filter data, right-click the table to be migrated in the Selected Objects box, and set the filter condition in the dialog box that appears. For instructions, see Set filter conditions. To select the SQL operations for incremental migration at the database or table level, right-click the migration object in the Selected Objects box, and select the desired SQL operations in the dialog box that appears.

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 as needed. This example does not require a tag.
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.

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.