Synchronizing PolarDB-X 2.0 to AnalyticDB MySQL 3.0 - Data Transmission Service

Prerequisites

A source PolarDB-X 2.0 instance has been created.
A destination AnalyticDB for MySQL V3.0 cluster has been created. For more information, see Create a cluster.
The storage space of the destination AnalyticDB for MySQL V3.0 cluster must exceed that of the source PolarDB-X 2.0 instance.

Usage notes

Note

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

Type	Description
Source database limits	Tables to be synchronized must have a primary key or a unique constraint, and the fields must be unique. Otherwise, duplicate data may appear in the destination database. Read-only instances of PolarDB-X 2.0 Enterprise Edition are not supported as the source. If you synchronize data at the table level and need to edit objects, such as mapping column names, and the number of tables in a single sync task exceeds 5,000, split the tables into multiple tasks. You can also configure a task to synchronize the entire database. Otherwise, an error may be reported after you submit the task. Binary logs: Enable binary logging in the PolarDB-X 2.0 console. For more information, see Parameter settings. Also, set binlog_row_image to full. Otherwise, the precheck fails and the data synchronization task cannot start. For incremental synchronization tasks, DTS requires that binary logs be retained on the source database for more than 24 hours. For tasks that include both initial full data synchronization and incremental synchronization, DTS requires that binary logs be retained for at least 7 days. You can change the retention period to more than 24 hours after the initial full data synchronization is complete. If binary logs are not retained for the required period, the DTS task may fail because it cannot obtain the logs. In extreme cases, this can lead to data inconsistency or data loss. Issues caused by binary log retention periods shorter than the DTS requirement are not covered by the Service-Level Agreement (SLA). If a table name in the PolarDB-X 2.0 instance contains uppercase letters, only schema synchronization is supported for that table. Synchronization of table groups and databases or tables with the Locality property is not supported. Synchronization of tables whose names are reserved words, such as `select`, is not supported. In a PolarDB-X 2.0 instance, database partitions in DRDS mode cannot be synchronized. Do not run DDL operations that change database or table schemas during schema synchronization or full synchronization. Otherwise, the synchronization task fails. Note During full synchronization, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database.
Other limits	Synchronization of prefix indexes is not supported. If the source database contains prefix indexes, the data synchronization may fail. The destination database must contain a custom primary key. Or, in the Configurations for Databases, Tables, and Columns step, configure a Primary Key Column. Otherwise, synchronization may fail. Due to the limits of AnalyticDB for MySQL, if the disk space usage of a node in the AnalyticDB for MySQL instance exceeds 80%, the DTS task becomes abnormal and latency occurs. Estimate the required space for the synchronization objects in advance 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 start data synchronization, evaluate the performance of the source and destination databases. We recommend that you perform data synchronization during off-peak hours. Initial full data synchronization consumes read and write resources on both the source and destination databases, which can increase database load. Initial full data synchronization runs concurrent INSERT operations, which causes fragmentation in the destination database tables. As a result, the tablespace of the destination instance is larger than that of the source instance after initial full data synchronization is complete. Do not use tools such as pt-online-schema-change to perform online DDL operations on the synchronization objects in the source database. Otherwise, the synchronization fails. During DTS synchronization, do not write data to the destination database from sources other than DTS. This can cause data inconsistency between the source and destination databases. For example, if you use DMS to perform online DDL operations while other data is being written to the destination database, data loss may occur in the destination database. If a DDL statement fails to be written to the destination database, the DTS task continues to run. You must check the task logs to find the failed DDL statement. For more information about how to view task logs, 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.
Other notes	DTS periodically updates the `dts_health_check`.`ha_health_check` table in the source database to advance the binary log offset.

Billing

Synchronization type	Pricing
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

Supported synchronization topologies

One-way one-to-one synchronization
One-way one-to-many synchronization
One-way cascade synchronization
One-way many-to-one synchronization

For more information, see Introduction to data synchronization topologies.

Supported SQL operations

Operation type	SQL statement
DML	`INSERT`, `UPDATE`, and `DELETE` Note When you write data to AnalyticDB for MySQL, it automatically converts `UPDATE` statements to `REPLACE INTO` statements. If you update a primary key, the system converts the `UPDATE` statement into `DELETE` and `INSERT` statements.
DDL	`CREATE TABLE`, `DROP TABLE`, `RENAME TABLE`, `TRUNCATE TABLE`, `ADD COLUMN`, `MODIFY COLUMN`, and `DROP COLUMN` Important The RENAME TABLE operation may cause data inconsistency. For example, if the synchronization object is a single table and you rename it on the source instance during synchronization, the data of that table is not synchronized to the destination database. To avoid this issue, you can configure the task to synchronize the entire database that contains the table. Make sure that the database to which the table belongs both before and after the RENAME TABLE operation is included in the synchronization objects.

Procedure

Go to the data synchronization task list page in the destination region. You can do this in one of two ways.
DTS console
1. Log on to the DTS console.
2. In the navigation pane on the left, click Data Synchronization.
3. In the upper-left corner of the page, select the region where the synchronization instance is located.
DMS console
Note
The actual steps may vary depending 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 DMS console.
2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.
3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.
Click Create Task to open the task configuration page.

Configure the source and destination databases.

Warning

After you select the source and destination instances, review the Limits 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	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	Database Type	Select PolarDB-X 2.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 2.0 instance is located.
	Replicate Data Across Alibaba Cloud Accounts	This tutorial uses an example of synchronization within the same Alibaba Cloud account. Select No.
	Instance ID	Select the ID of the source PolarDB-X 2.0 instance.
	Database Account	Enter the database account for the source PolarDB-X 2.0 instance. The account must have the REPLICATION SLAVE, REPLICATION CLIENT, and SELECT permissions on the synchronization objects. Note For more information about how to grant permissions, see Account permission issues during data synchronization.
	Database Password	Enter the password for the specified database account.
Destination Database	Select Existing Connection	Select the registered database instance with DTS from the drop-down list. The database information below is automatically configured. Note In the DMS console, this configuration item is Select a DMS database instance. If you have not registered the database instance or do not need to use a registered instance, manually configure the database information below.
	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 is located.
	Replicate Data Across Alibaba Cloud Accounts	This tutorial uses an example of synchronization within the same Alibaba Cloud account. Select No.
	Instance ID	Select the ID of the destination AnalyticDB for MySQL V3.0 cluster.
	Database Account	Enter the database account for the destination AnalyticDB for MySQL V3.0 cluster. The account must have read and write permissions.
	Database Password	Enter the password for the specified database account.

After you complete the configuration, click Test Connectivity and Proceed at the bottom of the page.
Note
Ensure that the IP address blocks of the DTS service are added to the security settings of the source and destination databases, either automatically or manually, to allow access from DTS servers. For more information, see Add the IP address whitelist of DTS servers.

Configure the task objects.

On the Configure Objects page, specify the objects to synchronize.

Parameter	Description
Synchronization Type	DTS always selects Incremental Data Synchronization. By default, you must also select Schema Synchronization and Full Data Synchronization. After the precheck, DTS initializes the destination cluster with the full data of the selected source objects, which serves as the baseline for subsequent incremental synchronization. Note If you select Full Data Synchronization, the schemas and data of the tables that are created by using the CREATE TABLE statement can be synchronized to the destination database.
Processing Mode for Existing Destination Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Database Table Column Name Mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
Table Merging	Select Yes: In online transactional processing (TP) scenarios, sharding is often used to improve the response speed of business tables. In online analytical processing (OLAP) scenarios, a single table in the destination database can store large volumes of data, which simplifies single-table queries. In such scenarios, you can use the DTS table merging feature to synchronize multiple tables with the same schema (sharded tables) from the source database to a single table in the destination database. For details on this operation, see Enable table merging. Note After you select multiple tables from the source database, you must use the object name mapping feature to change their names to the same table name in the destination database. For more information about the object name mapping feature, see Database Table Column Name Mapping. DTS adds a `__dts_data_source` column of the TEXT type to the destination table to store the data source. The column value is written in the `DTS instance ID:database name:schema name:table name` format to distinguish the source of the table, for example, `dts******:dtstestdata:testschema:customer1`. The table merging feature applies at the task level, not the table level. To merge only some tables, you must create a separate data synchronization task for them. Warning** Do not perform DDL operations that change the database or table schema in the source database. Otherwise, data inconsistency or task failure may occur. No: This is the default option.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select databases, tables, and columns as synchronization objects. If you select tables or columns as synchronization objects, DTS does not synchronize other objects such as views, triggers, and stored procedures to the destination database. If you select an entire database as the synchronization object, the following default rule applies: If a table to be synchronized in the source database has a primary key that contains one or more columns, DTS uses the primary key columns as the distribution key.
Selected Objects	To rename a single object in the destination instance, right-click the object in the Selected Objects box. For more information, see Map a single object name. To rename multiple objects in bulk, click Batch Edit in the upper-right corner of the Selected Objects box. For more information, see Map multiple object names in bulk. Note To select the SQL operations to synchronize for a specific database or table, right-click the object in the Selected Objects section and select the desired SQL operations in the dialog box that appears. To filter data by using WHERE conditions, right-click a table in the Selected Objects section and specify the filter conditions in the dialog box that appears. For more information, see Set filter conditions.

Click Next: Advanced Settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, 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 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
Environment Tag	You can select an environment tag to identify the instance based on your business requirements. In this tutorial, no tag is needed.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Choose whether DTS writes heartbeat SQL information to the source database while the instance is running. Yes: Does not write heartbeat SQL information to the source database. The DTS instance may display latency. No: Writes heartbeat SQL information to the source database. This may interfere with source database operations like physical backups and cloning.
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	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert notifications. For more information, see Configure monitoring and alerting during task configuration.

Optional: After you complete the configuration, 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 to sync in the destination database.
Note
- This step is available only if you select the Schema Synchronization checkbox for Synchronization Types during task object configuration. You can set Definition Status to All to make modifications.
- You can use the Primary Key Column to specify a composite primary key that consists of multiple columns. You must then select one or more columns from the Primary Key Column to serve as the Distribution Key and Partition Key. For more information, see CREATE TABLE.

Save the task and perform a precheck.
- To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.
- If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.
- If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.
- If the precheck generates warnings:
  For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.
  For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

Purchase the instance.

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

On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start, and then click OK in the OK dialog box.
You can monitor the task progress on the data synchronization page.