Migrate PolarDB for PostgreSQL (Oracle compatible) to AnalyticDB for MySQL V3.0 - Data Transmission Service

Prerequisites

You have a destination AnalyticDB for MySQL V3.0 cluster. For more information, see Create a cluster.
In the source PolarDB for PostgreSQL (Compatible with Oracle) cluster, the wal_level parameter must be set to logical. This setting adds the information required for logical decoding to the write-ahead logging (WAL). For more information, see Configure cluster parameters.

Limitations

Note

During schema migration, DTS does not migrate foreign keys from the source database to the destination database.
During full and incremental migration, DTS temporarily disables constraint checks and foreign key cascade operations at the session level. If cascade update or delete operations occur in the source database while the task is running, data inconsistency may occur.

Type	Description
Source database limits	Bandwidth requirement: 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 a primary key or a UNIQUE constraint. The fields in the key or constraint must have unique values. Otherwise, duplicate data may appear in the destination database. If you migrate data at the table level and need to edit objects, such as mapping table and column names, a single data migration task supports a maximum of 1,000 tables. If you exceed this limit, an error is reported after you submit the task. In this case, split the tables into multiple migration tasks, or configure a task to migrate the entire database. For incremental migration, the write-ahead log (wal) must be enabled. This must be enabled. For an incremental migration task, Data Transmission Service (DTS) requires that the wal logs 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 wal logs of the source database are retained for at least 7 days. You can set the log retention period to more than 24 hours after the full migration is complete. Otherwise, the DTS task may fail because DTS cannot obtain the wal logs. In extreme cases, data inconsistency or data loss may occur. Issues that are caused because the wal log retention period is shorter than the required period are not covered by the DTS Service-Level Agreement (SLA). 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 instance. Otherwise, data inconsistency occurs between the source and destination databases. To ensure real-time data consistency, select schema migration, full data migration, and incremental data migration. To ensure the migration task runs properly and to prevent logical subscription interruptions caused by a primary/secondary switchover, your PolarDB for PostgreSQL (Compatible with Oracle) instance must support and have Logical Replication Slot Failover enabled. For more information, see Enable Logical Replication Slot Failover. Note If the source PolarDB for PostgreSQL (Compatible with Oracle) cluster does not support the logical replication slot failover feature (for example, when the cluster's Database Engine is Oracle Syntax Compatible 2.0), the migration instance may fail and cannot be recovered when the source database triggers an HA failover. Due to the limits of logical replication in the source database, if a single piece of 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, the write-ahead logging (WAL) logs generated before the long-running transactions are committed cannot be purged. This causes the logs to accumulate and may lead to insufficient disk space in the source database.
Other limits	A single data migration task can migrate only one database. To migrate multiple databases, configure a data migration task for each database. The destination database must have a custom primary key. Or, in the Configurations for Databases, Tables, and Columns step, set the Primary Key Column. Otherwise, migration may fail. DTS does not support the migration of tables created by the TimescaleDB extension, tables with cross-schema inheritance, or tables with unique indexes based on expressions. 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 creates the following temporary tables in the source database to obtain DDL statements for incremental data, the schemas of incremental tables, and heartbeat information. Do not delete these temporary tables during the migration. Otherwise, the DTS task becomes abnormal. The temporary tables are automatically deleted after the DTS instance is released. `public.dts_pg_class`, `public.dts_pg_attribute`, `public.dts_pg_type`, `public.dts_pg_enum`, `public.dts_postgres_heartbeat`, `public.dts_ddl_command`, `public.dts_args_session`, and `public.aliyun_dts_instance`. To ensure the accuracy of the displayed migration latency for incremental data, DTS adds a heartbeat table named `dts_postgres_heartbeat` to the source database. 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. Due to the limits of AnalyticDB for MySQL 3.0, if the disk space usage of a node in the AnalyticDB for MySQL 3.0 cluster exceeds 80%, the DTS task becomes abnormal and latency occurs. 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 backing up while the DTS task runs, the task fails. Before you migrate data, evaluate the performance of the source and destination databases. We also recommend that you migrate data during off-peak hours. Otherwise, DTS consumes read and write resources on the source and destination databases during full data migration, which may increase the database load. Confirm whether the migration precision that DTS uses 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 you do not specify the precision, DTS migrates FLOAT columns with a precision of 38 and DOUBLE columns with a precision of 308. DTS attempts to resume failed migration tasks within seven days. Before you switch your business to the destination instance, make sure to end or release the task, or run the `revoke` command to revoke the write permissions of the account that DTS uses to access the destination instance. This prevents the source data from overwriting the data in the destination instance after the task is automatically resumed. If a DDL statement fails to be written to the destination database, the DTS task continues to run. You can view the failed DDL statement in the task logs. For more information, see Query task logs. 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. When migrating partitioned tables, include both the child partitions and the parent table as synchronization objects. Otherwise, data inconsistency may occur for the partitioned table. Note The parent table of a partitioned table in PolarDB for PostgreSQL (Compatible with Oracle) does not directly store data. All data is stored in the child partitions. The sync task must include both the parent table and all its child partitions. Otherwise, data from the child partitions may be missed, which leads to data inconsistency between the source and destination.

Billing

Migration type	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

Type	Description
Schema migration	DTS migrates the schema definitions of migration objects to the destination database. Currently, DTS supports schema migration only for tables.
Full data migration	DTS migrates all existing data within the migration objects from the source database to the destination database. Note Before the schema migration and full data migration are complete, do not perform DDL operations on the migration objects. Otherwise, the migration task may fail.
Incremental data migration	After the full data migration is complete, DTS captures incremental data updates from the source database's redo logs and migrates them to the destination database. Incremental data migration lets you migrate your data smoothly with minimal application downtime.

Supported SQL operations for incremental migration

Type	SQL statement
DML	INSERT, UPDATE, and DELETE Note When data is written to AnalyticDB for MySQL, UPDATE statements are automatically converted to REPLACE INTO statements. If the primary key is updated, the statement is converted to a DELETE statement and an INSERT statement.

Database account permissions

Database	Permissions	References
PolarDB for PostgreSQL (Compatible with Oracle) cluster	Requires a privileged account.	See Create a database account.
AnalyticDB for MySQL 3.0	Read and write permissions on the destination database.	See Create a database account.

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.

Warning

After you select the source and destination instances, we recommend that you carefully read the limits displayed at the top of the page. Otherwise, the task may fail or data inconsistency may occur.

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	Database Type	Select PolarDB (Compatible with Oracle).
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB for Oracle cluster resides.
	Instance ID	Select the instance ID of the source PolarDB for Oracle cluster.
	Database Name	Enter the name of the database that contains the objects to migrate from the source PolarDB for Oracle cluster.
	Database Account	Enter the database account of the source PolarDB for Oracle cluster. For information about the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the database account.
Destination Database	Database Type	Select AnalyticDB for MySQL 3.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination AnalyticDB for MySQL V3.0 cluster resides.
	Instance ID	Select the ID of the destination AnalyticDB for MySQL V3.0 cluster.
	Database Account	Enter the database account of the destination AnalyticDB for MySQL V3.0 cluster. For information about the required permissions, see Permissions required for database accounts.
	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 IP address segment of the DTS service is automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add DTS server IP addresses to a whitelist.
- If the source or destination database is a self-managed database (the Access Method is not Alibaba Cloud Instance), you must also click Test Connectivity in the CIDR Blocks of DTS Servers dialog box that appears.

Configure the task objects.

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

Parameter	Description
Migration Types	Select the migration types based on your requirements and the types supported by each engine. 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.
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.
DDL and DML Operations to Be Synchronized	Select the DDL or DML operations to migrate at the instance level. For a list of supported operations, see Supported SQL operations for incremental migration. Note To select SQL operations for incremental data migration at the table level, right-click the migration object in the Selected Objects box and select the required SQL operations in the dialog box that appears.
Merge Tables	If you select Yes, DTS adds the `__dts_data_source` column to each table to record data sources. For more information, see Enable multi-table merge. If you select No, this is the default option. Note The table merging feature is configured at the task level, not the table level. To merge some tables but not others, you must create two separate data migration tasks. Warning Do not perform DDL operations to change the schema of the source database or tables. Otherwise, data inconsistency or task failure may occur.
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. Important If you select Incremental Data Migration for Migration Types, you can select only a single table to migrate. If you do not select Incremental Data Migration for Migration Types, you can select objects at the database, table, or column level. If you select an entire database as the migration object, the following rules apply by default: If a table to be migrated in the source database has a primary key (single-column or multi-column), the primary key column is used as the distribution key. If a table to be migrated in the source database does not have a primary key, an auto-increment primary key column is automatically generated. This may cause data inconsistency between the source and destination databases.
Selected Objects	To change the name of a single migration object in the target instance, right-click the object in the Selected Objects box. For more information, see Map individual schema, table, and column names. To change the names of multiple migration objects in the target instance, click Selected Objects in the upper-right corner of the Batch Edit box. For more information, see Map multiple schema, table, and column names. Note If you use the object name mapping feature, other objects that depend on the renamed object may fail to be migrated. To filter data by using a WHERE clause, right-click the table to migrate in the Selected Objects box and specify the filter conditions in the dialog box that appears. For more information, see Set filter conditions. To select SQL operations to migrate at the database or table level, right-click the migration object in the Selected Objects box and select the required 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 based on your business requirements. This parameter 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 notifications. If a migration fails or the latency exceeds the threshold, the system sends an alert notification.

Click Next: Data Validation to configure a data validation task.

For more information about the data validation feature, see Configure data validation.
Optional: After you complete the preceding configurations, click Next: Configure Database and Table Fields to set the Type, Primary Key Column, Distribution Key, and partition key information (Partition Key, Partitioning Rules, and Partition Lifecycle) for the tables in the destination database.
Note
- This step is available only if you select Schema Migration for Migration Types. You can set Definition Status to All to modify the settings.
- You can select multiple columns for Primary Key Column to form a composite primary key. You must then select one or more columns from the Primary Key Column as the Distribution Key and Partition Key. For more information, see CREATE TABLE.

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.