how to synchronize data from an rds for mysql instance to a datahub project - Data Transmission Service

Alibaba Cloud DataHub is a platform for processing streaming data. It lets you publish, subscribe to, and distribute streaming data, which helps you easily build analytics and applications based on streaming data. You can use Data Transmission Service (DTS) to synchronize data from an RDS for MySQL instance to DataHub. This lets you quickly perform real-time data analysis using big data products, such as stream computing.

Prerequisites

A source RDS for MySQL instance is created.
Note
- For more information about how to create a source RDS for MySQL instance, see Create an RDS for MySQL instance.
- For more information about the supported versions, see Overview of data synchronization scenarios.
The DataHub service is activated, and a project has been created to receive the synchronized data. For more information, see Quick Start and Manage projects.

Notes

Note

DTS does not synchronize foreign keys from the source database to the destination database. Therefore, the cascade and delete operations on the source database are not synchronized to the destination database.

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 database may contain duplicate data records. If you select tables as the objects to be synchronized and you want to edit the tables, such as renaming tables or columns, 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 in batches or configure a task to synchronize the entire database. The following requirements for binary logs must be met: By default, the binary logging feature is enabled for an ApsaraDB RDS for MySQL instance. Make sure that the binlog_row_image parameter is set to full. Otherwise, error messages are returned during the precheck and the data synchronization task cannot be started. For more information, see Modify instance parameters. Important If the source database is a self-managed MySQL database, you must enable the binary logging feature and set the binlog_format parameter to row and the binlog_row_image parameter to full. If the source database is a self-managed MySQL database deployed in a dual-primary cluster, you must set the log_slave_updates parameter to ON. This ensures that DTS can obtain all binary logs. For more information, see Create an account for a self-managed MySQL database and configure binary logging. The binary logs of an ApsaraDB RDS for MySQL instance must be retained at least three days. We recommend that you set the retention period of the binary logs to seven days. The binary logs of the self-managed MySQL database must be stored for at least seven days. Otherwise, the data synchronization task may fail because DTS cannot obtain the binary logs. 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 ApsaraDB RDS for MySQL instance, see the Delete binary log files section in the topic "Manage binary log files". During schema synchronization and full data synchronization, do not execute DDL statements to change the schemas of databases or tables. Otherwise, the data synchronization task fails. The data generated by change operation of binary logs, such as data restored from a physical backup or data from a cascade operation, is not recorded or synchronized to the destination database when the data synchronization instance is running. Note If the change data is not recorded and synchronized to the destination database, you can modify the object to be synchronized and remove the databases and tables to which the data belongs on the premise that your business is not affected, and then add the databases and tables to which the data belongs to the object to be synchronized. For more information, see Modify the objects to be synchronized. If the source database is MySQL database 8.0.23 or later, and the data to be synchronized includes invisible columns, the data of the columns cannot be obtained and data loss occurs. Note To make the columns visible, run the `ALTER TABLE <table_name> ALTER COLUMN <column_name> SET VISIBLE;` command. For more information, see Invisible Columns. Tables that do not have primary keys automatically generate invisible primary keys. You need to make the invisible primary keys visible. For more information, see Generated Invisible Primary Keys.
Other limits	A single string in the destination DataHub project cannot exceed 2 MB in length. Indexes, partitions, views, procedures, functions, triggers, and foreign keys cannot be synchronized. If a table to be synchronized contains a column named record_id, we recommend that you use the object name mapping feature to rename the column in the destination database. Otherwise, an error is returned. For more information, see Map object names. Data inconsistency between the source and destination databases occurs if data from other sources is written to the destination database during the data synchronization. For example, if you use DMS to execute online DDL statements while data from other sources is written to the destination database, data loss may occur in the destination database. If the source database is an ApsaraDB RDS for MySQL instance for which the EncDB feature is enabled, full data synchronization cannot be performed. Note ApsaraDB RDS for MySQL instances that have the Transparent Data Encryption (TDE) feature enabled support schema synchronization, full data synchronization, and incremental data synchronization. If a DTS task fails to run, DTS technical support will try to restore the task within 8 hours. During the restoration, the task may be restarted, and the parameters of the task may be modified. Note Only the parameters of the DTS task may be modified. The parameters of databases are not modified. The parameters that may be modified include but are not limited to the parameters in the "Modify instance parameters" section of the Modify the parameters of a DTS instance topic.
Special cases	If the source database is a self-managed MySQL database, take note of the following items: If you perform a primary/secondary switchover on the source database when the data synchronization task is running, the task fails. DTS calculates synchronization latency based on the timestamp of the latest synchronized data in the destination database and the current timestamp in the source database. If no DML operation is performed on the source database for a long time, the synchronization latency may be inaccurate. If the latency of the data synchronization task is too high, you can perform a DML operation on the source database to update the latency. Note If you select an entire database as the object to synchronize, you can create a heartbeat table. The heartbeat table is updated or receives data every second. 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 the source database is an ApsaraDB RDS for MySQL instance, take note of the following item: An ApsaraDB RDS for MySQL instance that does not record transaction logs, such as a read-only ApsaraDB RDS for MySQL 5.6 instance, cannot be used as the source database. DTS executes the CREATE DATABASE IF NOT EXISTS 'test' statement in the source database as scheduled to move forward the binary log file position.

Supported synchronization topologies

One-way one-to-one synchronization.
One-way one-to-many synchronization.
One-way many-to-one synchronization.

For more information about the supported synchronization topologies, see Data synchronization topologies.

Supported SQL operations

Operation type	SQL operation
DML	INSERT, UPDATE, DELETE
DDL	ADD COLUMN Important If you manually modify the table schema in the destination database, you must restart the task. To do this, first pause and then start the task.

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.

Warning

After you configure the source and destination databases, we recommend that you read the Limits that are displayed on the page. Otherwise, the task may fail or data inconsistency may occur.

Category	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 a DMS database instance	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information.
	Database Type	Select MySQL.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the source RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	This example shows how to migrate data within the same Alibaba Cloud account. Select No.
	RDS Instance ID	Select the ID of the source RDS for MySQL instance.
	Database Account	Enter the database account of the source RDS for MySQL instance. The account must have the read permissions on the objects to be synchronized.
	Database Password	The password that is used to access the database.
	Encryption	Specifies whether to encrypt the connection to the database. You can select Non-encrypted or SSL-encrypted based on your business requirements. If you want to set this parameter to SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the DTS task. For more information, see Use a cloud certificate to enable SSL encryption.
Destination Database	Select a DMS database instance	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information.
	Database Type	Select DataHub.
	Access Method	Select Cloud Instance.
	Instance Region	Select the region where the DataHub instance resides.
	Project	Select the Project of the destination DataHub.

Click Test Connectivity and Proceed in the lower part of the page.
Note
- Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add the CIDR blocks of DTS servers.
- 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	The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization.
Naming Rules For Additional Columns	When DTS synchronizes data to DataHub, it adds some additional columns to the destination table. If the names of the additional columns conflict with the names of existing columns in the destination table, the data synchronization task fails. Select New Rule or Old Rule as required. Warning Before you select a naming rule, check whether the names of the additional columns conflict with the names of existing columns in the destination table. Otherwise, data loss or task failure may occur. For more information about the rules and definitions of additional columns, see Names and definitions of additional columns.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck, and the data synchronization task cannot be started. Note If the source and destination databases contain tables with identical names and the tables in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the tables that are synchronized to the destination database. For more information, see 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 schema and a data record in the destination database has the same primary key value or unique key value as a data record in the source database: During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, data may fail to be initialized. In this case, only some columns are synchronized, or the data synchronization instance fails. Proceed with caution.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select tables as the objects to be synchronized.
Selected Objects	To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see the "Map the name of a single object" section of the Map object names topic. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see the "Map multiple object names at a time" section of the Map object names topic. Note To specify WHERE conditions to filter data, right-click a table in the Selected Objects box and set the filter conditions in the dialog box that appears. For more information, see Set filter conditions. Right-click a table in the Selected Objects box. In the dialog box that appears, clear Synchronize All Tables. Then, you can set the Shardkey, which is the key used for partitioning.

Click Next: Advanced Settings to configure advanced settings.

Configuration	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.
Set Alerts	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.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set this parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range takes precedence. When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters for full data synchronization tasks to reduce the load on the destination database server. Note You can configure this parameter only if Full Data Synchronization is selected for the Synchronization Types parameter.
Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
Environment Tag	You can select an environment tag to identify the instance based on your requirements. In this example, you do not need to select a tag.
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.
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 the 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.

Topic schema definition

When DTS synchronizes data changes to a DataHub topic, it adds additional columns to the topic to store metadata in addition to the changed data. The following is an example.

Note

In this example, the business fields are id, name, and address. Because the old version of the naming rules for additional columns is used, DTS adds the dts_ prefix to the business fields.

Topic定义

Schema definition:

Old additional column name	New additional column name	Data type	Description
`dts_record_id`	`new_dts_sync_dts_record_id`	String	The unique ID of the incremental log record. Note By default, the ID auto-increments for each new log record. In disaster recovery scenarios, rollback may occur, and the ID may not auto-increment or be unique. If the operation type of the incremental log is UPDATE, the incremental update is split into two records, which record the before and after values respectively. The `dts_record_id` values are the same for both records.
`dts_operation_flag`	`new_dts_sync_dts_operation_flag`	String	The operation type. Valid values: I: INSERT operation. D: DELETE operation. U: UPDATE operation. F: Full data synchronization.
`dts_instance_id`	`new_dts_sync_dts_instance_id`	String	The server ID of the database.
`dts_db_name`	`new_dts_sync_dts_db_name`	String	The database name.
`dts_table_name`	`new_dts_sync_dts_table_name`	String	The table name.
`dts_utc_timestamp`	`new_dts_sync_dts_utc_timestamp`	String	The operation timestamp, which is the timestamp of the binary log (UTC time).
`dts_before_flag`	`new_dts_sync_dts_before_flag`	String	Indicates whether all column values are the values before the update. Valid values: Y and N.
`dts_after_flag`	`new_dts_sync_dts_after_flag`	String	Indicates whether all column values are the values after the update. Valid values: Y and N.

Additional information about dts_before_flag and dts_after_flag

The values of dts_before_flag and dts_after_flag in an incremental log record vary based on the operation type:

INSERT
For an INSERT operation, all column values are the newly inserted values, which are the values after the operation. Therefore, the value of dts_before_flag is N and the value of dts_after_flag is Y. The following is an example.
UPDATE
For an UPDATE operation, DTS splits the operation into two incremental log records. These two log records have the same values for dts_record_id, dts_operation_flag, and dts_utc_timestamp.
The first incremental log record contains the values before the update. Therefore, the value of dts_before_flag is Y and the value of dts_after_flag is N. The second incremental log record contains the values after the update. Therefore, the value of dts_before_flag is N and the value of dts_after_flag is Y. The following is an example.
DELETE
For a DELETE operation, the incremental log contains the values of the deleted record. Therefore, the value of dts_before_flag is Y and the value of dts_after_flag is N. The following is an example.