how to migrate data from polardb for mysql to kafka - Data Transmission Service

This topic describes how to use Data Transmission Service (DTS) to migrate data from a PolarDB for MySQL cluster to a Kafka cluster to extend your message processing capabilities.

Preparations

You have created a target self-managed Kafka cluster or a Message Queue for Apache Kafka instance.
Note
- If the destination instance is a Message Queue for Apache Kafka instance, you must create a topic to receive the migrated data. Then, you must configure the instance as a self-managed Kafka cluster. For more information about how to create a topic, see Step 1: Create a topic.
- For information about the supported versions of the source and destination databases, see Migration solutions.
The destination Kafka cluster must have more available storage space than the storage space occupied by the source PolarDB for MySQL cluster.

Notes

Note

DTS does not migrate foreign keys in the source database to the destination database. Therefore, the cascade and delete operations of the source database are not migrated to the destination database.

Type	Description
Source database limits	The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the data migration speed is affected. The tables to migrate must have primary keys or UNIQUE constraints, and the fields must be unique. Otherwise, duplicate data may exist in the destination database. If you select tables as the migration objects and need to edit them, such as mapping table or column names, you can migrate a maximum of 1,000 tables in a single task. To migrate more than 1,000 tables, we recommend that you split the tables and configure multiple tasks to migrate them in batches. You can also configure a task to migrate the entire database. Otherwise, a request error may be reported after you submit the task. You cannot migrate data from read-only nodes of the source cluster. If you need to migrate 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 the precheck and the data migration task fails to 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 stored for at least three days. We recommend that you store the binary logs 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. Make sure that you configure the retention period of binary logs based on the preceding requirements. Otherwise, the service reliability or performance stated in the Service Level Agreement (SLA) of DTS may not be guaranteed. Note For more information about how to set retention period of the binary logs of a PolarDB for MySQL cluster, see Modify the retention period. During schema migration and full data migration, do not perform DDL operations to change the database or table schemas. Otherwise, the data migration task fails. Note During full data migration, DTS queries the source database. This creates metadata locks, which may block DDL operations from being executed on the source database. If you perform only full data migration, do not write new data to the source database. Otherwise, data becomes inconsistent between the source and destination databases. To ensure real-time data consistency, we recommend that you select Schema Migration, Full Data Migration, and Incremental Data Migration.
Other limits	DTS does not migrate the read-only nodes of the source PolarDB for MySQL cluster. DTS does not migrate Object Storage Service (OSS) external tables from the source PolarDB for MySQL cluster. You cannot migrate INDEX, PARTITION, VIEW, PROCEDURE, FUNCTION, TRIGGER, and FK objects. DTS does not support active/standby switchover for the database instance during full data migration. If a switchover occurs, reconfigure the migration task right away. Do not use tools such as pt-online-schema-change to perform online DDL operations on the migration objects in the source database. Otherwise, the migration fails. For columns of the FLOAT or DOUBLE data type, DTS uses `ROUND(COLUMN,PRECISION)` to read the values of these columns. If you do not explicitly define the precision, DTS uses a precision of 38 for the FLOAT data type and 308 for the DOUBLE data type. Confirm that the migration precision meets your business requirements. Before you migrate data, evaluate the performance of the source and destination databases. We also recommend that you migrate data during off-peak hours. This is because during full data migration, DTS consumes some read and write resources of the source and destination databases, which may increase the database load. DTS attempts to resume tasks for instances that have failed within the last seven days. Therefore, before you switch your workloads to the destination instance, you must end or release the instance. You can also use the `REVOKE` command to revoke the write permissions from the database account that DTS uses to access the destination instance. This prevents the task from being automatically resumed, which would cause data in the source database to overwrite data in the destination instance. 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.
Other notes	DTS periodically runs the CREATE DATABASE IF NOT EXISTS `test` command in the source database to advance the binary log offset. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. Therefore, after full data migration is complete, the table storage space in the destination database is larger than that in the source instance.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	When the Access Method parameter of the destination database is set to Public IP Address, you are charged for Internet traffic. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration type descriptions

Schema migration
DTS migrates the schemas of the selected objects from the source database to the destination database.
Full data migration
DTS migrates the historical data of required objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting the services of self-managed applications during data migration.

SQL operations that can be incrementally migrated

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE
DDL	CREATE TABLE, ALTER TABLE, DROP TABLE, RENAME TABLE, TRUNCATE TABLE

Permissions required for database accounts

Database	Permission requirement	How to create and grant permissions to an account
PolarDB for MySQL cluster	Read permissions on the objects to migrate	Create and manage a database account

Procedure

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation 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 > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration 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.

Category	Configuration	Description
None	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify an informative 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 Cloud Instance.
	Instance Region	Select the region where the source PolarDB for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	In this example, data is migrated within the same Alibaba Cloud account. Select No.
	PolarDB Instance ID	Select the ID of the source PolarDB for MySQL instance.
	Database Account	Enter the database account of the source PolarDB for MySQL instance. For information about the required permissions, see Permissions required for database accounts.
	Database Password	The password that is used to access the database instance.
	Encryption	Specifies whether to encrypt the connection to the source database. You can configure this parameter based on your business requirements. For more information about the SSL encryption feature, see Configure 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 Kafka.
	Access Method	Select a connection type based on the deployment location of the destination instance. This topic uses Self-managed Database On ECS as an example. Note If the destination instance is a self-managed database, you must also perform the required preparations. For more information, see Preparation overview.
	Instance Region	Select the region where the destination Kafka cluster resides.
	ECS Instance ID	Select the ID of the destination Kafka cluster.
	Port	Enter the service port of the destination Kafka cluster. The default value is 9092.
	Database Account	Enter the username of the Kafka cluster. You can leave this blank if authentication is not enabled for the Kafka cluster.
	Database Password	Enter the password for the username of the Kafka cluster. You can leave this blank if authentication is not enabled for the Kafka cluster.
	Kafka Version	Select the version of the Kafka cluster. Note If the version of the self-managed Kafka cluster is 1.0 or later, you can set Kafka Version to 1.0 Or Later.
	Encryption	Based on your business and security requirements, select Non-encrypted Connection or SCRAM-SHA-256.
	Topic	From the drop-down list, select the topic that receives data.
	Use Kafka Schema Registry	Kafka Schema Registry is a service layer for metadata. It provides a RESTful interface for storing and retrieving Avro schemas. No: Do not use Kafka Schema Registry. Yes: Use Kafka Schema Registry. You need to enter the URL or IP address that is registered in Kafka Schema Registry for the Avro schema.

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 migrated.

On the Configure Objects page, configure the objects that you want to migrate.

Configuration	Description
Migration Types	If you only need to perform full migration, we recommend that you select Schema Migration and Full Data Migration. To perform migration without service interruption, we recommend that you select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If the Access Method of the destination Kafka instance is Alibaba Cloud Instance, Schema Migration is not supported. If you do not select Schema Migration, ensure that the destination database contains the database and tables to receive the data. Then, use the object name mapping feature in the Selected Objects box if required. If you do not select Incremental Data Migration, do not write new data to the source instance during data migration to ensure data consistency.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that use 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 migration 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 migrated to the destination database. 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 the following potential risks: If the source and destination databases have the same schema, and a data record has the same primary key as an existing data record in the destination database, the following scenarios may occur: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates 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, only specific columns are migrated or the data migration task fails. Proceed with caution.
Data Format In Kafka	Select the data storage format for the data migrated to the Kafka instance. If you select DTS Avro, data is parsed based on the schema definition of DTS Avro. For more information, see GitHub. If you select Canal JSON, for information about the parameters and examples of Canal JSON, see Canal JSON. If you select Shareplex JSON, for information about the parameters and examples of Shareplex JSON, see Shareplex JSON.
Kafka Data Compression Format	The compression format for Kafka compressed data. Select a compression format based on your business requirements. Valid values: LZ4: (default): low compression ratio and high compression speed. GZIP: high compression ratio and low compression speed. Note GZIP compression consumes a large quantity of CPU resources. Snappy: medium compression ratio and medium compression speed.
Policy for Shipping Data to Kafka Partitions	Select a policy based on your requirements.
Message acknowledgement mechanism	Select a message acknowledgment mechanism based on your requirements.
Topic That Stores DDL Information	From the drop-down list, select the topic used to store DDL information. Note If you do not select a topic, the DDL information is stored in the topic that receives data by default.
Capitalization of Object Names in Destination Instance	You can configure the case-sensitivity policy for the names of migrated databases, tables, and columns in the destination instance. By default, DTS Default Policy is selected. You can also select a policy that is consistent with the default policy of the source or destination database. For more information, see Case-sensitivity of object names in the destination database.
Source Objects	Select one or more objects from the Source Objects section. Click the icon and add the objects to the Selected Objects section. Note You can select objects at the table level.
Selected Objects	No additional configuration is required in this example. You can use the mapping feature to set the topic name, number of partitions for the topic, and partition key for the source table in the destination Kafka instance. For more information, see Mapping information. Note If you use the object name mapping feature, other objects that depend on the mapped object may fail to be migrated. To select the SQL operations for incremental migration, right-click the migration object in the Selected Objects box. In the dialog box that appears, select the SQL operations for incremental migration.

Click Next: Advanced Settings to configure advanced settings.

Configuration	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration 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 migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1,440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified later 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 database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration 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 Migration	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must 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. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
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 as needed. No selection is required in this example.
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 migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure 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 migration task, DTS performs a precheck. You can start the data migration 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 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 issues. Then, run a precheck again.
  If the 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 the instance.

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

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
- If a data migration task cannot be used to migrate incremental data, the task automatically stops. The Completed is displayed in the Status section.
- If a data migration task can be used to migrate incremental data, the task does not automatically stop. The incremental data migration task never stops or completes. The Running is displayed in the Status section.

Mapping information

In the Selected Objects section, move the mouse pointer over the destination topic name (at the table level).
Click Edit that appears next to the destination topic name.

In the Edit Table dialog box that appears, configure the mapping information.