Synchronize data from a PolarDB for MySQL cluster to an AnalyticDB for MySQL V3.0 cluster - Data Transmission Service

This topic describes how to synchronize data from a PolarDB for MySQL cluster to an AnalyticDB for MySQL V3.0 cluster by using Data Transmission Service (DTS). After you synchronize data, you can use AnalyticDB for MySQL to build internal business intelligence (BI) systems, interactive query systems, and real-time report systems.

Prerequisites

The source PolarDB for MySQL cluster is created. For more information, see Purchase a pay-as-you-go cluster and Purchase a subscription cluster.
The destination AnalyticDB for MySQL V3.0 cluster is created. For more information, see Create a cluster.
The available storage space of the destination AnalyticDB for MySQL cluster is larger than the total size of the data in the source PolarDB for MySQL cluster.

Usage notes

Note

During schema synchronization, DTS synchronizes foreign keys from the source database to the destination database.
During full synchronization and incremental synchronization, DTS temporarily disables checking of foreign key constraints and foreign key cascade operations 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	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 may contain duplicate data records. If you select tables as the objects to be synchronized and you need to edit the tables, such as renaming tables or columns, in the destination database, you can synchronize up to 1,000 tables in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables or configure a task to synchronize the entire database. If you need to synchronize incremental data, the binary logging feature must be enabled and the loose_polar_log_bin parameter must be set to on. Otherwise, error messages are returned during precheck and the data synchronization task cannot be started. For more information about how to enable the binary logging feature and set the loose_polar_log_bin parameter, see Enable binary logging and Modify parameters. Note If you enable the binary logging feature for a PolarDB for MySQL cluster, you are charged for the storage space that is occupied by binary logs. For an incremental data synchronization task, the binary logs of the source database are retained for at least 24 hours. For a full and incremental data synchronization task, the binary logs of the source database are retained for at least seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. 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 based on the preceding requirements. Otherwise, the SLA of DTS does not guarantee service reliability or performance. During data synchronization, do not perform DDL operations to modify the primary key or add comments because the operations cannot take effect. For example, do not execute the `ALTER TABLE table_name COMMENT='Table comments';` statement.
Other limits	Prefix indexes cannot be synchronized. If the source database contains prefix indexes, data may fail to be synchronized. Read-only nodes of the source PolarDB for MySQL cluster cannot be synchronized. Due to the limits of AnalyticDB for MySQL clusters, if the disk space usage of the nodes in an AnalyticDB for MySQL cluster reaches 80%, the data synchronization task is delayed and error messages are returned. We recommend that you estimate the required disk space based on the objects that you want to synchronize. You must ensure that the destination cluster has sufficient storage space. 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 tablespace of the destination database is larger than that of the source database. We recommend that you do not use tools such as pt-online-schema-change to perform DDL operations on source tables during data synchronization. Otherwise, data synchronization may fail. If you use only DTS to write data to the destination database, you can use Data Management (DMS) to perform online DDL operations on source tables during data synchronization. For more information, see Perform lock-free operations. 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.
Usage notes	DTS executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database as scheduled to move forward the binary log file position.

Billing


Synchronization type	Task configuration fee
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 many-to-one synchronization

SQL operations that can be synchronized


Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE Note When data is written to the AnalyticDB for MySQL cluster, the UPDATE statement is automatically converted to the REPLACE INTO statement.
DDL	CREATE TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE, ADD COLUMN, and DROP COLUMN

Warning If the data type of a field in the source table is changed during data synchronization, an error message is returned and the data synchronization task is interrupted. You can perform the following steps to troubleshoot the issue:

When DTS synchronizes data to the destination AnalyticDB for MySQL cluster, the data type of a field in the source table is changed. As a result, the data synchronization task fails. In this example, the source table is named customer.
In the destination AnalyticDB for MySQL V3.0 cluster, create a table named customer_new that has the same schema as the customer table.
Execute the INSERT INTO SELECT statement to copy the data of the customer table and insert the data into the customer_new table. This ensures that the data of the two tables is consistent.
Rename or delete the customer table. Then, change the name of the customer_new table to customer.
Start the data synchronization task again in the DTS console.

Procedure

Go to the Data Synchronization Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
Note
- Operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Configure the DMS console based on your business requirements.
- You can also go to the Data Synchronization Tasks page of the new DTS console.
From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Note If you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.

Click Create Task. On the page that appears, configure the source and destination databases.

Warning After you select the source and destination instances, we recommend that you read the limits displayed in the upper part of the page. This helps you create and run the data synchronization task.


Section	Parameter	Description
N/A	Task Name	DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name.
Source Database	Select Instance	Select whether to use an existing instance. If you select an existing instance, DTS automatically applies the parameter settings of the instance. You do not need to configure the corresponding parameters again. If you do not use an existing instance, you must configure parameters for the source database.
	Database Type	The type of the source database. Select PolarDB for MySQL.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source PolarDB for MySQL cluster resides.
	PolarDB Cluster ID	The ID of the source PolarDB for MySQL cluster.
	Database Account	The database account of the source PolarDB for MySQL cluster. The account must have the read permissions on the objects to be synchronized.
	Database Password	The password of the database account.
Destination Database	Select Instance	Select whether to use an existing instance. If you select an existing instance, DTS automatically applies the parameter settings of the instance. You do not need to configure the corresponding parameters again. If you do not use an existing instance, you must configure parameters for the source database.
	Database Type	The type of the destination database. Select AnalyticDB for MySQL V3.0.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	Select 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	Enter the database account of the destination AnalyticDB for MySQL V3.0 cluster. The account must have the read and write permissions on the destination database.
	Database Password	The password of the database account.

In the lower part of the page, click Test Connectivity and Proceed.
Warning
- If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you need to manually add the CIDR blocks of DTS servers to the whitelist of the self-managed database on the ECS instance to allow DTS to access the database. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database.
- If the CIDR blocks of DTS servers are automatically or manually added to the whitelist or ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
- After the DTS task is complete or released, we recommend that you manually remove the CIDR blocks of DTS servers from the whitelist or ECS security group rules. You must remove the IP address whitelist group whose name contains dts from the whitelist of the Alibaba Cloud database instance or the security group rules of the ECS instance. For more information about the CIDR blocks that you must remove from the whitelist of the self-managed databases that are deployed in data centers or databases that are hosted on third-party cloud services, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

Select objects for the task and configure advanced settings.


Parameter	Description
Task Stages	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 database. 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.
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 You can use the object name mapping feature to rename the tables that are synchronized to the destination database. You can use this feature if the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed. For more information, see Map object names. 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 schemas, and a data record has the same primary key value as an existing data record in the destination 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.
DDL and DML Operations to Be Synchronized	The DDL and DML operations that you want to synchronize. For more information, see the SQL operations that can be synchronized section of this 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.
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 make sure 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.
Merge Tables	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. To do this, you can use the object name mapping feature. For more information, see Map object names. 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. DTS specifies the column values based on the following format: `<DTS instance ID>:<Database name>:<Schema name>:<Table name>`. Such column values allow DTS to identify each source table. For example, `dts******:dtstestdata:testschema:customer1` indicates that the source table is customer1. If you set this parameter to Yes, all the selected source tables in the task are merged into a single 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 may occur or the data synchronization task fails. No: This is the default value.
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 columns, tables, or databases as the objects to be synchronized. If you select tables or columns as the objects to be synchronized, DTS does not synchronize other objects such as views, triggers, or stored procedures to the destination database. If you select a database as the object to be synchronized, DTS synchronizes data based on the following default rules: If the table to be synchronized in the source database has a primary key, such as a single-column primary key or a composite primary key, the primary key columns are specified as the distribution keys. If the table to be synchronized in the source database does not have a primary key, an auto-increment primary key column is automatically generated in the destination table. This may cause data inconsistency between the source and destination databases.
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 Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note To select the SQL operations performed on a specific database or table, right-click an object to be synchronized in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information about the SQL operations that can be synchronized, see the SQL operations that can be synchronized section of this topic. 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 Use SQL conditions to filter data.

Click Next: Advanced Settings to configure advanced settings.


Parameter	Description
Set Alerts	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 configure alerting. Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see Configure monitoring and alerting when you create a DTS task.
Copy the temporary table of the Online DDL tool that is generated in the source table to the destination database	In this scenario, DTS does not synchronize DDL operations. You must set this parameter to No, Adapt to DMS Online DDL or No, Adapt to gh-ost. However, DTS may support DDL operation synchronization for this scenario in the future. In this case, if you use DMS or the gh-ost tool to perform online DDL operations on the source database, you can specify whether to synchronize temporary tables generated by online DDL operations. Valid values: Yes: DTS synchronizes the data of temporary tables generated by online DDL operations. Note If online DDL operations generate a large amount of data, the data synchronization task may take an extended period of time to complete. No, Apply to DMS Online DDL: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL operations that are performed by using DMS are synchronized. Note If you select this option, the tables in the destination database may be locked. No, Adapt to gh-ost: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL operations that are performed by using the gh-ost tool are synchronized. You can use the default or custom regular expressions to filter out the shadow tables of the gh-ost tool and tables that are not required. Note If you select this option, the tables in the destination database may be locked.
Retry Time for Failed Connection	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 the 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 set different retry time ranges for multiple DTS tasks that have the same source or destination database, the shortest retry time range that is set takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source and destination instances are released.
Configure ETL	Specifies whether to configure 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.
Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, specific features such as physical backup and cloning of the source database may be affected.

In the lower part of the page, click Next: Configure Database and Table Fields. On the page that appears, set the primary key columns and distribution key columns of the tables that you want to synchronize to the destination AnalyticDB for MySQL cluster.
Note
- If you select Schema Synchronization as Task Stages, you must configure the Type, Primary Key Column, and Distribution Key parameters for the tables that you want to synchronize to the AnalyticDB for MySQL V3.0 cluster. For more information, see CREATE TABLE.
- 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 primary key columns as the distribution keys.
In the lower part of the page, click Next: Save Task Settings and Precheck.
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 task fails to pass the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
- If an alert is generated for an item during the precheck, perform the following operations based on the scenario:
  
  In scenarios where you cannot ignore the alert item, click View Details next to the failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
  
  In scenarios where you can ignore the alert item, click Confirm Alert Details next to the failed item. 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.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance 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 the instance when you create an 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 charged 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 instance, you can release the pay-as-you-go instance to reduce costs.
	Instance Class	DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class based on your business scenario. For more information, see Specifications of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months or one to three years. Note This parameter is displayed only if you select the subscription billing method.

Read and select the check box for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.