Data migration between AnalyticDB for PostgreSQL instances-Data Transmission Service(DTS)-阿里云帮助中心

Prerequisites

A target AnalyticDB for PostgreSQL instance has been created with enough storage space to hold the data from the source AnalyticDB for PostgreSQL instance.
A database has been created in the target AnalyticDB for PostgreSQL instance for the migrated data.

Notes

Source database limitations

Bandwidth requirement: The server that hosts the source database must have an outbound bandwidth of 100 Mbit/s or higher. Otherwise, the data migration speed is affected.
The kernel version of the source AnalyticDB for PostgreSQL instance must be 7.2.1.4 or later.
Parameter settings for the source database:
- You must enable logical decoding by setting the wal_level parameter to logical.
- If the instance edition of the source AnalyticDB for PostgreSQL instance is High-availability Edition, you must set the hot_standby, hot_standby_feedback, and sync_replication_slots parameters to on. This ensures that the migration task runs as expected and prevents logical subscriptions from being interrupted by a primary/standby switchover.
Requirements for migration objects:
- The name of the database to be migrated cannot contain hyphens (-), such as dts-testdata.
- Each table to be migrated must have a primary key or a unique constraint. For a unique constraint, the constrained columns must not contain duplicate values. Otherwise, duplicate data may occur in the target database.
- DTS does not support migrating the following objects: tables with cross-schema inheritance relationships, temporary tables, internal system triggers (TRIGGER), some functions (such as C-language functions and internal functions for PROCEDURE and FUNCTION), and extensions (EXTENSION). However, DTS does support migrating some custom data types (COMPOSITE, ENUM, or RANGE) and the following constraints: primary key, unique, and CHECK.
- If you use schema migration on a partitioned table, its partitioning information is lost, and the table is created as a non-partitioned table in the target database.
- If you migrate objects at the table level and need to edit them, such as mapping table or column names, a single migration task supports a maximum of 5,000 tables. If you exceed this limit, the task fails after submission. In this case, split the tables into multiple migration tasks or configure a task to migrate the entire database.
Operational limits for the source database:
- During schema migration and full data migration, do not perform DDL operations that change the database or table schema. Otherwise, the data migration task fails.
  
  Note
  During full data migration, DTS queries the source database. This creates a metadata lock, which may block DDL operations on the source database.
- 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.
If the source database has long-running transactions and the instance performs incremental migration, the write-ahead logs (WALs) generated before the long-running transactions are committed cannot be cleared. This may cause the WALs to accumulate and exhaust the disk space of the source database.

Other limitations

A single migration task can migrate data from only one database. To migrate multiple databases, you must configure a separate migration task for each one.
DTS does not support migrating DDL operations from the source database.
After schema migration, the account used for the migration task becomes the owner of all schemas and tables in the target database.
If a source table has a primary key, it is preserved in the target database. If a source table lacks a primary key, its distribution key becomes the primary key in the target database by default.
If a table to be migrated contains a SERIAL column, the source database automatically creates a sequence for that column. Therefore, when you configure the 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 performs incremental data migration, 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 ensures data consistency. This requirement applies in the following two scenarios. During the execution of this command, do not perform table lock operations to avoid deadlocks. If you skip the related 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 validates data content but does not support the validation of metadata such as sequences. You must validate the metadata yourself.
Before the switchover, you must query the maximum value of each sequence in the source database and then use this value as the initial value for the corresponding sequence in the target database. The following command queries the sequence values in the source database:
```
do language plpgsql $$
declare
  nsp name;
  rel name;
  val int8;
begin
  for nsp,rel in select nspname,relname from pg_class t2 , pg_namespace t3 where t2.relnamespace=t3.oid and t2.relkind='S'
  loop
    execute format($_$select last_value from %I.%I$_$, nsp, rel) into val;
    raise notice '%',
    format($_$select setval('%I.%I'::regclass, %s);$_$, nsp, rel, val+1);
  end loop;
end;
$$;
```
Note
The SQL statements that are returned after you run the preceding command contain all sequences in the source database. Run these statements in the target database based on your business requirements.
To ensure the accuracy of the displayed migration latency for incremental data, DTS adds a heartbeat table named dts_postgres_heartbeat to the source database.
Data Transmission Service (DTS) creates the following temporary tables in the source database to obtain the DDL statements of incremental data, the schemas of incremental tables, and heartbeat information. During data migration, do not delete temporary tables in the source database. Otherwise, the data migration task may fail. 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.
During incremental data migration, DTS creates a replication slot with the dts_sync_ prefix 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 whitelist from 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 full data migration, DTS consumes read and write resources on both the source and target databases, which can increase their load. Before migrating, evaluate the performance of both databases and run the migration during off-peak hours, for example, when the CPU utilization of both databases is below 30%.
Full data migration performs concurrent INSERT operations, which can cause table fragmentation in the target database. As a result, the target tables may occupy more storage space than the source tables after the migration.
While the migration task is running:
- Do not change the connection endpoint or availability zone of the AnalyticDB for PostgreSQL instance. Otherwise, the migration task will fail.
- If any process other than DTS writes data to the target database during migration, this may cause data inconsistency or even cause the migration task to fail.
If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters.

Note
Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.

Billing

Migration type	Link configuration fees	Data transfer fees
Schema migration + full data migration	Free	Free (unless the destination access method is Public IP Address — see Billing overview)
Incremental data migration	Charged — see Billing overview	—

Supported objects

SCHEMA, TABLE

Note
Tables include PRIMARY KEY, UNIQUE KEY, DATATYPE (built-in data type), and DEFAULT CONSTRAINT.
VIEW, INDEX, PROCEDURE, FUNCTION, RULE, SEQUENCE, AGGREGATE, OPERATOR, DOMAIN

Supported SQL for incremental migration

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE

Database account permission requirements

Database	Required permissions	Actions
Source AnalyticDB for PostgreSQL instance	Read and `REPLICATION` permissions for the objects to be migrated. `ALTER USER your_user WITH REPLICATION;`	Create and manage users Note You can grant the `REPLICATION` permission by running the `ALTER USER <username> WITH REPLICATION;` command.
Destination AnalyticDB for PostgreSQL instance	Read and write permissions on the destination database.	Create and manage users Note You can use the initial account or an account with the `RDS_SUPERUSER` role.

Procedure

Navigate to the migration task list page for the destination region using 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 menu 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.
Click Create Task to navigate to the task configuration page.

Configure the source and destination databases.

Category	Parameter	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 need 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 AnalyticDB for PostgreSQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the source AnalyticDB for PostgreSQL instance.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database instance under the current Alibaba Cloud account is used. Select No.
	Instance ID	Select the instance ID of the source AnalyticDB for PostgreSQL instance.
	Database Name	Enter the name of the database in the source AnalyticDB for PostgreSQL instance to migrate.
	Database Account	Enter the database account for the source AnalyticDB for PostgreSQL instance.
	Database Password	Enter the password for 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 AnalyticDB for PostgreSQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region of the destination AnalyticDB for PostgreSQL instance.
	Instance ID	Select the instance ID of the destination AnalyticDB for PostgreSQL instance.
	Database Name	Enter the name of the database in the destination AnalyticDB for PostgreSQL instance to receive the migrated data.
	Database Account	Enter the database account for the destination AnalyticDB for PostgreSQL instance.
	Database Password	Enter the password for the database account.

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

Note
Ensure that the DTS service IP address segments are 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.

Configure the task objects.

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

Parameter	Description
Migration Types	If you only need to perform a full migration, select both Schema Migration and Full Data Migration. To perform a migration with no downtime, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If you do not select Schema Migration, you must ensure that a database and tables to receive the data exist in the destination database. You can also use the object name mapping feature in the Selected Objects box as needed. If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.
DDL and DML Operations to Be Synchronized	Select the SQL operations for incremental migration at the instance level based on your requirements. Note To select SQL operations for incremental migration at the schema or table level, right-click the migration object in the Selected Objects box below and select the desired SQL operations in the dialog box that appears.
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 is passed. If tables with the same names exist, an error is reported during the precheck, 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 database. The record from the source database is not migrated. During incremental migration, DTS does not keep the record in the destination database. 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.
Storage Engine Type	Select a storage engine for the destination tables based on your business requirements. The default value is Beam. Note This parameter is available only if the destination AnalyticDB for PostgreSQL instance has a kernel version of v7.0.6.6 or later and you selected Migration Types for the Schema Migration parameter.
Capitalization of Object Names in Destination Instance	You can configure the case sensitivity policy for the 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 the case sensitivity 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 to move them to the Selected Objects box. Note You can select migration objects at the schema or table level.
Selected Objects	To set the name of a migration object in the destination instance, or to specify the object that receives data in the destination instance, right-click the migration object in the Selected Objects box to make changes. For more information, see Object name mapping. To remove a selected migration object, click the object in the Selected Objects box, and then click to move it to the Source Objects box. Note If you use the object name mapping feature, other objects that depend on the mapped object may fail to migrate. To set a WHERE clause to filter data, right-click the table to migrate in the Selected Objects box and set the filter condition in the dialog box that appears. For more information about how to set the condition, see Set filter conditions. To select the SQL operations for incremental migration, 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 parameters.

Parameter	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 begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1440 minutes. We recommend that you set the duration to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified duration, 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 a non-connectivity issue, such as a DDL or DML execution exception, occurs in the source or destination database, DTS reports an error and immediately begins to retry the operation. The default retry duration is 10 minutes. You can customize the retry time to a value from 1 to 1440 minutes. We recommend that you set the duration to more than 10 minutes. If the related operations succeed within the specified retry duration, 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 full migration, DTS consumes read and write resources on the source and destination databases, which may increase the database load. If required, you can enable throttling 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 load 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	If required, you can also choose 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 load 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. 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: Yes: Enables the ETL feature. Enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: Disables the ETL feature.
Monitoring and Alerting	Select whether to set alerts and receive alert notifications based on your business needs. No: Does not set an alert. Yes: Configure alerts by setting an alert threshold and an alert contact. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

Optional: After you complete the preceding settings, click Next: Configure Database and Table Fields to configure the Type, Primary Key Column, and Distribution Key for the migrated tables in the destination AnalyticDB for PostgreSQL instance.
Note
- This step is available only if you select Schema Migration for Migration Types when you configure task objects. You can set Definition Status to All to make modifications.
- The Primary Key Column can be a composite key that consists of multiple columns. You must select one or more columns from the Primary Key Column to serve as the Distribution Key. For more information, see Manage data tables and Table distribution definition.

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 that appears.
- 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, DTS performs a precheck. 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, 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 ignore a warning, it may cause issues such as data inconsistency and pose risks to your business.

Purchase the instance.

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

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?
New Instance Class	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.

After the configuration is complete, read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the OK dialog box that appears, click OK.

You can view the progress of the migration task on the Data Migration Tasks list page.
Note
- If the migration task does not include incremental migration, it stops automatically after the full migration is complete. After the task stops, its Status changes to Completed.
- If the migration task includes incremental migration, it does not stop automatically. The incremental migration task continues to run. While the incremental migration task is running, the Status of the task is Running.