Synchronize data from a PolarDB for MySQL cluster to a Lindorm instance - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to synchronize data from a PolarDB for MySQL cluster to the wide table engine of a Lindorm instance.

Prerequisites

You have created a destination Lindorm instance that uses the LindormTable engine. The available storage space of the destination Lindorm instance must exceed the storage space used by the source PolarDB for MySQL cluster. For more information, see Create an instance.
You have enabled the MySQL compatibility feature for the destination Lindorm instance. For more information, see Enable the MySQL compatibility feature.
You have created a database (namespace) and a wide table in the destination Lindorm instance to receive the synchronized data. The wide table must be pre-partitioned to accommodate the full data. For more information, see Use a MySQL client to connect to and use LindormTable, Use Lindorm-cli to connect to and use the wide table engine, Use Lindorm Shell to access LindormTable, CREATE TABLE, and Data type mapping.
Note
The object you created must meet the requirements specified in Quotas and limits.

Usage notes

Category	Description
Source database limits	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. If you select tables as the objects to be synchronized and you need to modify 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. The following requirements for binary logs must be met: 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 the precheck and a DTS task cannot be started. For more information, 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. The binary logs of a PolarDB for MySQL cluster must be retained at least three days. We recommend that you set the retention period of the binary logs to seven days. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you configure the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability or performance in the Service Level Agreement (SLA) of DTS may not be guaranteed. Note For more information about how to set the Retention Period of the binary logs for an PolarDB for MySQL cluster, see the Modify the retention period section in the topic "Enable binary logging". During full data synchronization, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data synchronization task fails. Note During full data synchronization, DTS queries the source database. This creates metadata locks, which may block DDL operations on the source database.
Other limits	Schema synchronization is not supported. You cannot synchronize data of the BIT type. You cannot synchronize only primary key fields. The data to be synchronized must contain at least one non-primary key field. DTS does not synchronize the read-only nodes of the source PolarDB for MySQL cluster. DTS does not synchronize Object Storage Service (OSS) external tables from the source PolarDB for MySQL cluster. DTS does not support primary/secondary switchover of database instances during full data synchronization. If a switchover occurs, reconfigure the synchronization task. You can write data only to the wide table engine of the Lindorm instance. If the data to be synchronized contains empty strings of the VARBINARY type, the empty strings of the VARBINARY type are processed as null values in DTS and Lindorm instance. If the fields of the DECIMAL type that receive data in the destination Lindorm instance and the fields in the source instance have different precision, the task fails. The data to be synchronized in the Lindorm instance must meet the requirements specified in Limits on data requests. Otherwise, the task fails. During initial full data synchronization, DTS uses some read and write resources of the source and destination databases. This may increase the database server load. Before you synchronize data, evaluate the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. For example, you can synchronize data when the CPU load of the source and destination databases is below 30%. During initial full data synchronization, concurrent INSERT operations cause table fragmentation in the destination database. After the initial full data synchronization is complete, the table storage space used by the destination database is larger than that of the source database. During data synchronization, do not use tools such as pt-online-schema-change to perform online DDL operations on the synchronized objects in the source database. Otherwise, the synchronization fails. If data from sources other than DTS is written to the destination database during data synchronization, data inconsistency may occur between the source and destination databases. DTS executes the CREATE DATABASE IF NOT EXISTS `test` statement in the source database as scheduled to move forward the binary log file position. If an instance fails, DTS helpdesk will try to recover the instance within 8 hours. During the recovery process, operations such as restarting the instance and adjusting parameters may be performed. Note When parameters are adjusted, only the parameters of the DTS instance are modified. The parameters of the database are not modified. The parameters that may be modified include but are not limited to those described in Modify instance parameters.

Billing

Synchronization type	Link Configuration Fees
Full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

SQL operations that support incremental synchronization

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE
DDL	CREATE TABLE, DROP TABLE, and ADD COLUMN Note Due to the limitations of the destination LindormTable engine, DTS does not synchronize extra attributes in ADD COLUMN statements. For example, if you run the `ALTER TABLE test ADD COLUMN col INT DEFAULT 0;` statement on a synchronized object in the source database, DTS runs the `ALTER TABLE test ADD COLUMN col INT;` statement on the destination database.

Permissions required for database accounts

Database	Required permissions	Creation and authorization
Source PolarDB for MySQL cluster	Read and write permissions	Create and manage a database account
Destination Lindorm	Read and write permissions on the destination namespace	Manage users

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 task 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	Configuration	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.
Source Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select PolarDB for MySQL.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the source PolarDB for MySQL cluster resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
	PolarDB Cluster ID	Select the ID of the source PolarDB for MySQL cluster.
	Database Account	Enter the database account of the source PolarDB for MySQL cluster. For more information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database.
	Encryption	Select a method as needed. For more information about the SSL encryption feature, see Set SSL encryption.
Destination Database	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	Select Lindorm.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination Lindorm instance resides.
	Instance ID	Select the ID of the destination Lindorm instance.
	Database Account	Enter the database account of the destination Lindorm instance. For more information about the required permissions, 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 DTS server IP addresses to a whitelist.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be synchronized.

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

Configuration	Description
Synchronization Types	By default, Incremental Data Synchronization is selected. You can select only Full Data Synchronization. You cannot select Schema 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.
Processing Mode of Conflicting Tables	You do not need to configure this parameter. Use the default value.
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 columns, tables, and databases as the objects to be synchronized.
Selected Objects	If the names of the databases (namespaces), tables, or columns that you created in the destination Lindorm instance are different from the names of the objects to be synchronized from the PolarDB for MySQL cluster, you must use the object name mapping feature. For more information, see Map object names. Note If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be synchronized. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Specify filter conditions. To select SQL operations for incremental synchronization, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize.

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 instances, 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.
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. Valid values: 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, features such as physical backup and cloning of the source database may be affected.
Environment Tag	You can select an environment tag to identify the instance if required. In this example, you do not need to select a 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 instance. 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.

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 task. 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.