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

This topic describes how to use Data Transmission Service (DTS) to synchronize data from a PolarDB-X 1.0 instance to an AnalyticDB for MySQL 3.0 cluster and achieve real-time incremental data synchronization.

Prerequisites

You have created a PolarDB-X 1.0 instance. If not, see Create a PolarDB-X 1.0 instance and Create a database.

Note
The storage for the PolarDB-X 1.0 instance must be ApsaraDB RDS for MySQL, which can be either a privately customized or a separately purchased RDS instance. PolarDB for MySQL is not supported.
Ensure that the character set of the data to be synchronized is not utf8mb3. Otherwise, the incremental data synchronization task will fail.
You have created a destination AnalyticDB for MySQL 3.0 cluster. The cluster must have more available storage space than the source PolarDB-X 1.0 instance uses. If you have not created a cluster, see Create a cluster.

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.

Category	Description
Limits on the source database	The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints (tables that have only UNIQUE constraints do not support schema synchronization, so we recommend that you use PRIMARY KEY constraints), and the fields must be unique. Otherwise, the destination database may contain duplicate data. 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 mapping table or column names, 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 may occur after you submit the task. In this case, we recommend that you split the tables to be synchronized and 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 RDS for MySQL instances attached to the PolarDB-X 1.0 instance must be met: The binary logging feature must be enabled, and the binlog_row_image parameter must be set to full. Otherwise, an error is reported during the precheck, and the data synchronization task cannot be started. For an incremental synchronization task, DTS requires that the binary logs of the source database be retained for at least 24 hours. For a task that performs both full and incremental synchronization, DTS requires that the binary logs of the source database be retained for at least seven days. You can set the retention period of binary logs to more than 24 hours after the initial full data synchronization is complete. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data may be inconsistent or lost. Issues that are caused because the retention period of binary logs is shorter than the required period are not covered by the DTS Service-Level Agreement (SLA). 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 connectivity information of the synchronization link after the network type is changed. During data synchronization, do not scale the source instance, such as scaling the attached RDS for MySQL instance or changing the distribution of physical databases and tables that correspond to logical databases and tables in the RDS for MySQL instance even if the RDS for MySQL instance is not scaled. In addition, do not migrate hot spot tables, change shard keys, or perform DDL operations. Otherwise, the data synchronization task fails or data inconsistency occurs. 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. The storage class of the PolarDB-X 1.0 instance must be RDS for MySQL, including private custom RDS and separately purchased RDS. PolarDB for MySQL is not supported as the storage class. Storage resources of PolarDB-X 1.0 can be split only using horizontal splitting (sharding). Vertical splitting is not supported. Read-only instances of PolarDB-X 1.0 computing resources are not supported. The version of the source PolarDB-X 1.0 instance must be 5.2 or later.
Other limits	Indexes, partitions, views, procedures, functions, triggers, and foreign key constraints (FKs) are not synchronized. 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. DTS ensures the data consistency of incremental synchronization tasks based on the continuity of XA transactions in the source PolarDB-X 1.0 instance. If the continuity of XA transactions is disrupted, for example, when you modify the synchronization objects or in disaster recovery scenarios for the incremental data collection module, uncommitted XA transactions may be lost. A data synchronization task for a PolarDB-X 1.0 instance is a distributed task. A subtask is created for each attached RDS for MySQL instance. You can view the running status of subtasks in the Task Topology. If the destination AnalyticDB for MySQL 3.0 cluster is backing up while the DTS task runs, the task fails. Before you synchronize data, you must evaluate the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. Otherwise, initial full data synchronization may consume read and write resources of the source and destination databases and increase database loads. During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. Therefore, after initial full data synchronization is complete, the tablespace of the destination instance is larger than that of the source instance. 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 data synchronization, do not write data to the destination database using other tools. Otherwise, data inconsistency between the source and destination databases occurs. For example, if you use DMS to perform online DDL operations when data is written to the destination database using other tools, data may be lost in the destination database. 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.

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.

Permissions required for database accounts

Database	Required permissions	Creation and authorization
Source PolarDB-X 1.0 instance	Read permissions on the objects to be synchronized.	Account management
Destination AnalyticDB for MySQL 3.0 cluster	Read and write permissions on the destination database where the objects will be synchronized.	Create a database account.

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.

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-X 1.0.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB-X 1.0 instance is located.
	Replicate Data Across Alibaba Cloud Accounts	For this example, select No, as the database instance belongs to the current Alibaba Cloud account.
	Instance ID	Select the ID of the source PolarDB-X 1.0 instance.
	Database Account	Enter the database account for the source PolarDB-X 1.0 instance. For the required permissions, see Permissions required for database accounts.
	Database Password	Enter the password for the specified 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 3.0 cluster is located.
	Instance ID	Select the ID of the destination AnalyticDB for MySQL 3.0 instance.
	Database Account	Enter the database account for the destination AnalyticDB for MySQL 3.0 cluster. For the required permissions, see Permissions required for database accounts.
	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 Types	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.
DDL and DML Operations to Be Synchronized	Select the SQL operations for incremental data synchronization at the instance level. For a list of supported operations, see Supported SQL operations. Note To select SQL operations at the database or table level, right-click a synchronization object in the Selected Objects section and select the desired SQL operations in the dialog box that appears.
Merge Tables	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.
Processing Mode of Conflicting 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.
Capitalization of Object Names in Destination Instance	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note We recommend that you select objects at the table level. If you select an entire database as a synchronization object, changes to add or delete tables in the source database are not synchronized to the destination database.
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 SQL operations at the database or table level, right-click a synchronization 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 to be synchronized 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. For this example, you do not need to select a tag.
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.