Migrate data from PolarDB for MySQL to AnalyticDB for PostgreSQL - Data Transmission Service

Use Data Transmission Service (DTS) to migrate data from a PolarDB for MySQL instance to an AnalyticDB for PostgreSQL instance.

Prerequisites

A destination AnalyticDB for PostgreSQL instance is created. For more information, see Create an instance.
The destination AnalyticDB for PostgreSQL instance must have more available storage space than the storage space used by the source PolarDB for MySQL cluster instance.

Notes

Note

During schema migration, DTS migrates 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.

Category	Description
Limits on the source database	Bandwidth requirements: The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. The tables to be migrated must have primary keys or UNIQUE constraints, and the fields in the tables must be unique. Otherwise, duplicate data may exist in the destination database. If you migrate objects at the table level and need to edit them, such as by mapping column names, a single migration task can migrate a maximum of 1,000 tables. To migrate more than 1,000 tables, split the tables into multiple migration tasks. You can also configure a migration task for the entire database. Otherwise, a request error may be reported after you submit the task. If you need to migrate incremental data: The binary logging feature must be enabled and the loose_polar_log_bin parameter must be set to on. Otherwise, error messages are returned during the precheck and the data migration task fails to be started. For more information, see Enable binary logging and Modify parameters. Note If you enable the binary logging feature for a PolarDB for MySQL cluster, you are charged for the storage space that is occupied by binary logs. The binary logs of a PolarDB for MySQL cluster must be stored for at least three days. We recommend that you store the binary logs seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you configure the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability or performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed. Note For more information about how to set retention period of the binary logs of a PolarDB for MySQL cluster, see Modify the retention period. During schema migration and full migration, do not perform DDL operations to change the database or table structure. Otherwise, the data migration task fails. Note During full migration, DTS queries the source database. This creates metadata locks, which may block DDL operations on the source database. 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 Migration. If the data to be migrated from the source database contains the date value `0000-00-00 00:00:00`, the task may fail. Note DTS converts this date value to `null` when migrating it to the destination database. You can temporarily change the source data to `0001-01-01 00:00:00` or allow null values for the corresponding column in the destination database.
Other limits	You cannot migrate data from read-only nodes of the source PolarDB for MySQL instance. DTS does not migrate Object Storage Service (OSS) external tables from the source PolarDB for MySQL cluster. Migration of partitions, views, stored procedures, functions, triggers, foreign keys, and indexes is not supported. Only table-level migration is supported. Destination tables cannot be append-optimized (AO) tables. DTS does not support primary/secondary switchover of the database instance during full migration. If a switchover occurs, reconfigure the migration task promptly. If the source database undergoes online DDL changes that use temporary tables, such as multi-table merges, data loss may occur in the destination database or the migration instance may fail. If you use column mapping for a partial table migration, or if the source and destination table structures are inconsistent, data in columns that exist in the source but not the destination is lost. If a table to be migrated contain a primary key, the primary key column in the destination table must be the same as that of the source table. If a table to be migrated does not contain a primary key, the primary key column and the distribution key in the destination table must be the same. A unique key (primary key column contained) in the destination table must contain all columns of its distribution key. During full data migration, DTS consumes read and write resources of the source and destination databases. This may increase the loads on the database servers. Before you migrate data, evaluate the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. For columns of the FLOAT or DOUBLE data type, DTS uses `ROUND(COLUMN,PRECISION)` to read the values of these columns. If you do not define the precision, DTS uses a precision of 38 for FLOAT columns and 308 for DOUBLE columns. Confirm that the migration precision meets your business requirements. DTS tries to resume tasks that failed within the last seven days. Before you switch your business to the destination instance, end or release the instance. You can also run the `REVOKE` command to revoke the write permissions from the database account that DTS uses to access the destination instance. This prevents the task from being automatically resumed, which would cause data in the source instance to overwrite data in the destination instance. 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.
Other notes	DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command in the source database to advance the binary log offset. Full data migration involves concurrent INSERT operations, which cause fragmentation in the tables of the destination database. After full data migration is complete, the storage space that is used by tables in the destination database is larger than that in the source instance.

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

Schema migration
DTS migrates the schema definitions of migration objects from the source database to the destination database.
Full migration
DTS migrates all historical data of migration objects from the source database to the destination database.
Incremental migration
After full migration, DTS migrates incremental data updates from the source database to the destination database. Incremental migration lets you migrate data smoothly without stopping your applications.

Supported SQL operations for incremental migration

Operation type	SQL operation
DML	INSERT, UPDATE, DELETE Note When data is written to the destination AnalyticDB for PostgreSQL instance, the UPDATE statement is automatically converted to the REPLACE INTO statement. If the UPDATE statement is executed on primary keys, the UPDATE statement is converted to the DELETE and INSERT statements.
DDL	CREATE TABLE, ALTER TABLE, TRUNCATE TABLE, DROP TABLE

Database account permissions

Database	Required permissions	How to create an account and grant permissions
PolarDB for MySQL cluster	Read permissions on the migration objects	Create and manage a database account
AnalyticDB for PostgreSQL	Read and write permissions on the destination database to which the migration objects belong	Create and manage a user Note Alternatively, you can use an account that has RDS_SUPERUSER permissions. For more information about how to create this account, see User permission management.

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.

Section	Parameter	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 PolarDB for MySQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the source PolarDB for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	This example migrates data within the same Alibaba Cloud account. Select No.
	PolarDB Instance ID	Select the ID of the source PolarDB for MySQL instance.
	Database Account	Enter the database account of the source PolarDB for MySQL instance. For more information about the required permissions, see Database account permissions.
	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. For more information about the SSL encryption feature, see Configure 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 AnalyticDB PostgreSQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the destination AnalyticDB for PostgreSQL instance resides.
	Instance ID	Select the ID of the destination AnalyticDB for PostgreSQL instance.
	Database Name	Enter the name of the database to which the migration objects belong in the destination AnalyticDB for PostgreSQL instance.
	Database Account	Enter the database account of the destination AnalyticDB for PostgreSQL instance. For more information about the required permissions, see Database account permissions.
	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	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 Error: Checks for tables in the destination database that have the same names as tables in the source database. If no such tables exist, the precheck passes. If tables with the same name exist, the precheck fails and the data migration task does not start. Note If you cannot delete or rename the tables with the same name in the destination database, you can change their names in the destination database. For more information, see Map object names. Clear Destination Table Data: Clears the existing data from the destination tables. Select this option with caution. Ignore Error and Continue: Skips the check for tables with the same name in the destination database. Warning If you select Ignore Error and Continue, data inconsistency may occur, which poses risks to your business. For example: If the table structures are consistent and the destination database contains a record with the same primary key value as a record in the source database: During full migration, DTS retains 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 retain the record in the destination cluster. The record from the source database overwrites the record in the destination database. If the table structures are inconsistent, data initialization may fail, only partial data may be migrated, or the migration may fail.
DDL and DML Operations to Be Synchronized	Select the SQL operations for incremental migration at the instance level. For more information about the supported operations, see Supported SQL operations for incremental migration. Note To select the SQL operations for incremental migration at the database or table level, right-click a migration object in the Selected Objects section. In the dialog box that appears, select the SQL operations to migrate.
Capitalization of Object Names in Destination Instance	The capitalization policy for the names of databases, tables, and columns in the destination instance. The default is DTS Default Policy. You can also select a policy that matches the default policy of the source or destination database. For more information, see Capitalization of destination object names.
Storage Engine Type	The storage engine type of the destination table. Default value: Beam. Specify this parameter based on your business requirements. Note This parameter is available only the minor version of the destination AnalyticDB for PostgreSQL instance is v7.0.6.6 or later and you specify Schema Migration for the Migration Types parameter.
Source Objects	Select one or more objects from the Source Objects section. Click the icon and add the objects to the Selected Objects section. Note You can select columns, tables, or schemas as the objects to be migrated. If you select tables or columns as the objects to be migrated, DTS does not migrate other objects, such as views, triggers, or stored procedures, to the destination database.
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, the migration of other objects that depend on the renamed object may fail. To set a WHERE clause to filter data, right-click the table to migrate in the Selected Objects section and set the filter condition in the dialog box that appears. For more information, see Set filter conditions. To select the SQL operations to migrate at the database or table level, right-click the migration object in the Selected Objects section 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.
Copy the temporary table of the Online DDL tool that is generated in the source table to the destination database	If you use DMS or the gh-ost tool to perform online DDL operations on the source database, you can specify whether to migrate the data of temporary tables generated by online DDL operations. Valid values: Important You cannot use tools such as pt-online-schema-change to perform online DDL operations on the source database. Otherwise, the DTS task fails. Yes: DTS migrates the data of temporary tables generated by online DDL operations. Note If online DDL operations generate a large amount of data, latency may occur for the data migration task. No, Adapt to DMS Online DDL: DTS does not migrate the data of temporary tables generated by online DDL operations. Only the original DDL operations that are performed by using DMS are migrated. Note If you select this option, the tables in the destination database may be locked. No, Adapt to gh-ost: DTS does not migrate the data of temporary tables generated by online DDL operations. Only the original DDL operations that are performed by using the gh-ost tool are migrated. You can use the default or custom regular expressions to filter out the shadow tables of the gh-ost tool and tables that are not required. Note If you select this option, the tables in the destination database may be locked.
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.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Valid values: Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, features such as physical backup and cloning of the source database may be affected.
Environment Tag	You can select an environment tag to identify the instance. This example does not require a selection.
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.

After you complete the configuration, click Next: Configure Database And Table Fields at the bottom of the page to set the primary key and distribution key columns for the tables in the destination AnalyticDB for PostgreSQL instance.
Note
This page appears only if you select Schema Migration for the Migration Types parameter. For more information about primary key and distribution key columns, see Table management and Table distribution.

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.