Synchronize data from PolarDB-X 1.0 to AnalyticDB for MySQL 3.0 - Data Transmission Service

This topic describes how to synchronize incremental data in real time from a PolarDB-X 1.0 instance to an AnalyticDB for MySQL V3.0 cluster by using Data Transmission Service (DTS).

Prerequisites

The source PolarDB-X 1.0 instance is created. For more information, see Create a PolarDB-X 1.0 instance and Create a database.
Note
The storage type of the PolarDB-X 1.0 instance must be ApsaraDB RDS for MySQL (private custom RDS instance or purchased RDS instance). PolarDB for MySQL cannot be used as the storage type.
The character set of the data to be synchronized from the source database is not utf8mb3. Otherwise, an incremental data synchronization task fails.
The destination AnalyticDB for MySQL V3.0 cluster is created. The available storage space of this cluster is larger than the total size of the data in the source PolarDB-X 1.0 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 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 synchronization, data inconsistency may occur.

Category	Migration description
Limits on the source database	The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints and all fields must be unique. Otherwise, the destination database may contain duplicate data records. The tables that only have UNIQUE constraints do not support schema synchronization. Therefore, we recommend that you synchronize the tables that have PRIMARY KEY constraints. Tables that have secondary indexes cannot be synchronized. If you select tables as the objects to be synchronized and you want to edit the tables (such as renaming tables or columns) in the destination database, you can synchronize up to 5,000 tables in a single data synchronization task. If you run a task to synchronize more than 5,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database. The following requirements for binary logs of the ApsaraDB RDS for MySQL instances attached to the PolarDB-X 1.0 instance must be met: The binary logging feature is enabled. The value of the binlog_row_image parameter is set to full. Otherwise, error messages are returned during the precheck and the data synchronization task cannot be started. For an incremental data synchronization task, the binary logs of the source database must be retained for at least 24 hours. For a full and incremental data synchronization task, the binary logs of the source database must be retained for at least seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data may be inconsistent or lost. After full data synchronization is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of binary logs in accordance with the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS cannot be achieved. Limits on operations to be performed on the source database: If you change the network type of the PolarDB-X 1.0 instance during data synchronization, you must modify the network connection information of the data synchronization task after you change the network type. During data synchronization, do not scale the source instance, including the ApsaraDB RDS for MySQL instance attached to the source instance, or change the distribution of physical databases for which a logical database or logical table has been configured in the ApsaraDB RDS for MySQL instance. In addition, do not migrate hot tables, change the shard keys, or perform online DDL operations on the source instance. Otherwise, the data synchronization task fails or data inconsistency occurs. The storage type of the PolarDB-X 1.0 instance must be ApsaraDB RDS for MySQL, including custom instances and purchased instances. PolarDB for MySQL cannot be used as the storage type. PolarDB-X 1.0 storage resources can be split only by using horizontal splitting. Both databases and tables can be split. Vertical splitting is not supported. Read-only instances at the PolarDB-X 1.0 compute layers are not supported.
Other limits	When DTS synchronizes data from a PolarDB-X 1.0 instance, data is distributed across the attached ApsaraDB RDS for MySQL instances. DTS runs a subtask for each ApsaraDB RDS for MySQL instance. The running state of the subtask is displayed in Task Topology. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. During initial full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the loads on the database servers. During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is complete, the size of used tablespace of the destination database is larger than that of the source database. We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects to be synchronized. Otherwise, data synchronization may fail. During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases. If you use tools other than DTS to write data to the destination database, data loss may occur in the destination database when you use DMS to perform online DDL operations.

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 about the synchronization topologies that are supported by DTS, see Synchronization topologies.

SQL operations that can be synchronized

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE. Note When data is written to the destination AnalyticDB for MySQL V3.0 cluster, the UPDATE statement is automatically converted to the REPLACE INTO statement. If the UPDATE statement is executed on the primary key, the UPDATE statement is converted to the DELETE and INSERT statements.

Permissions required for database accounts

Database	Required permission	References
Source PolarDB-X 1.0 instance	The read permissions on the objects to be synchronized	Manage accounts
Destination AnalyticDB for MySQL V3.0 cluster	The read and write permissions on the database to which the objects to be synchronized belong	Create a database account

Procedure

Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Synchronization.
3. In the upper-left corner of the page, select the region in which the data synchronization instance resides.
DMS console
Note
The actual operations 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 and choose DTS (DTS) > Data Synchronization.
3. From the drop-down list to the right of Data Synchronization 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 a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
	Database Type	The type of the source database. Select PolarDB-X 1.0.
	Access Method	The access method of the source instance. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source PolarDB-X 1.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
	Instance ID	The ID of the source PolarDB-X 1.0 instance.
	Database Account	The database account of the source PolarDB-X 1.0 instance. For information about the permissions that are required for the account, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.
	Database Type	The type of the destination database. Select AnalyticDB for MySQL 3.0.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination AnalyticDB for MySQL V3.0 cluster resides.
	Instance ID	The ID of the destination AnalyticDB for MySQL V3.0 cluster.
	Database Account	The database account of the destination AnalyticDB for MySQL V3.0 cluster. For more information about the permissions that are required for the account, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.

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 the CIDR blocks of DTS servers.

Configure the objects to be synchronized.

In the Configure Objects step, configure the objects that you want to synchronize.

Parameter	Description
Synchronization Types	The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization. Note If Full Data Synchronization is selected, you can synchronize the schema and data of the table that is created by executing the CREATE TABLE statement to the destination database.
DDL and DML Operations to Be Synchronized	The DDL and DML operations that you want to synchronize. For more information, see SQL operations that can be synchronized. Note To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize.
Merge Table	Yes: In online transaction processing (OLTP) scenarios, sharding is implemented to speed up the response to business tables. In online analytical processing (OLAP) scenarios, you can store a large volume of data in a single table. This makes your SQL queries more efficient. You can merge multiple source tables that have the same schema into a single destination table. This feature allows you to synchronize data from multiple tables in the source database to a single table in the destination database. For more information, see Enable the multi-table merging feature. Note After you select multiple tables from the source database, you must change the names of these tables to the name of the destination table by using the object name mapping feature. For more information, see Database, table, and column name mapping. DTS adds a column named `__dts_data_source` to the destination table. This column is used to record the data source. The data type of this column is TEXT. The values of this column are in the following format: `data synchronization instance ID:source database name:source schema name:source table name`. This allows DTS to identify each source table. Example: `dts******:dtstestdata:testschema:customer1`. If you set this parameter to Yes, all the selected source tables in the task are merged into the destination table. If you do not need to merge specific source tables, you can create a separate data synchronization task for these tables. Warning** We recommend that you do not perform DDL operations to change the schemas of source databases or tables. Otherwise, data inconsistency occurs or the data synchronization task fails. No: This value is selected by default.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck, and the data synchronization task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are synchronized to the destination database. For more information, see Database, table, and column name mapping. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to potential risks. If the source and destination databases have the same schema and a data record in the destination database has the same primary key value or unique key value as a data record in the source database: During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, data may fail to be initialized. In this case, only some columns are synchronized, or the data synchronization task fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select tables as the objects to be synchronized. If you select an entire database as the object to be synchronized, DTS does not synchronize the changes made to create tables in or delete tables from the source database to the destination database.
Selected Objects	To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the "Individual database, table, and column name mapping" section of the Map object names topic. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the "Batch database, table, and column name mapping" section of the Map object names topic. Note To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. To specify WHERE conditions to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information about how to specify the conditions, see Specify filter conditions.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set this parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range 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 your earliest opportunity after the source and destination instances are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization 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 Synchronization	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can 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 for full data synchronization tasks to reduce the load on the destination database server. Note You can configure this parameter only if Full Data Synchronization is selected for the Synchronization Types parameter.
Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, you do not need to select an environment tag.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not enable 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.

Optional: In the lower part of the page, click Next: Configure Database and Table Fields. In the page that appears, configure the Type, Primary Key Column, Distribution Key, and partition key information such as Partition Key, Partitioning Rules, and Partition Lifecycle for the tables to be synchronized in the destination database.
Note
- If you set the Synchronization Types You can perform this step only if you select Schema Synchronization for the Synchronization Types parameter. To modify the parameters, set the Definition Status parameter to All.
- In the Primary Key Column field, you can specify multiple columns to form a composite primary key. In this case, you must specify one or more columns as the Distribution Key and Partition Key. For more information, see CREATE TABLE.

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 synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.
- If the data synchronization task fails the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, rerun the precheck.
- 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 issue. Then, run a precheck again.
  If an 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 an instance.

Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the buy page, configure the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go data synchronization instance, you can release the instance to reduce costs.
	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start. In the dialog box that appears, click OK.
You can view the progress of the task in the task list.