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Data Transmission Service:Synchronize data from a PolarDB-X 1.0 instance to a DataHub project

Last Updated:Dec 22, 2023

This topic describes how to synchronize data from a PolarDB-X 1.0 instance to a DataHub project by using Data Transmission Service (DTS).

Prerequisites

  • DataHub is activated, and a project is created to receive the data to be synchronized. For more information, see Get started with DataHub and Manage projects.

  • The available storage space of the destination DataHub project is larger than the total size of the data in the source PolarDB-X 1.0 instance.

Limits

Note

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

Category

Migration 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. The tables that only have UNIQUE constraints do not support schema synchronization. Therefore, we recommend that you synchronize the tables that have PRIMARY KEY constraints. Tables that have secondary indexes cannot be synchronized.

  • If you select tables as the objects to be synchronized and you want to edit the tables (such as renaming tables or columns) in the destination database, you can synchronize up to 5,000 tables in a single data synchronization task. If you run a task to synchronize more than 5,000 tables, a request error 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 of the ApsaraDB RDS for MySQL instances attached to the PolarDB-X 1.0 instance must be met:

    • The binary logging feature is enabled. The value of 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 an incremental data synchronization task, the binary logs of the source database must be retained for at least 24 hours. For a full and incremental data synchronization task, the binary logs of the source database must be retained for at least seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data may be inconsistent or lost. 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 in accordance with the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS cannot be achieved.

  • Limits on operations to be performed on the source database:

    • If you change the network type of the PolarDB-X 1.0 instance during data synchronization, you must modify the network connection information of the data synchronization task after you change the network type.

    • During data synchronization, do not scale the source instance, including the ApsaraDB RDS for MySQL instance attached to the source instance, or change the distribution of physical databases for which a logical database or logical table has been configured in the ApsaraDB RDS for MySQL instance. In addition, do not migrate hot tables, change the shard keys, or perform online DDL operations on the source instance. Otherwise, the data synchronization task fails or data inconsistency occurs.ApsaraDB RDS for MySQL

  • The storage type of the PolarDB-X 1.0 instance must be ApsaraDB RDS for MySQL, including custom instances and purchased instances. PolarDB for MySQL cannot be used as the storage type.

  • PolarDB-X 1.0 storage resources can be split only by using horizontal splitting. Both databases and tables can be split. Vertical splitting is not supported.

  • Read-only instances at the PolarDB-X 1.0 compute layers are not supported.

Other limits

  • Only incremental data synchronization and schema synchronization are supported. Full data synchronization is not supported.

  • Limits on the objects to be synchronized:

    • Only tables can be selected as the objects to be synchronized.

    • After a data synchronization task is started, DTS does not synchronize columns that are created in the source database to the destination DataHub project.

  • When DTS synchronizes data from a PolarDB-X 1.0 instance, data is distributed across the attached ApsaraDB RDS for MySQL instances. DTS runs a subtask for each ApsaraDB RDS for MySQL instance. The running state of the subtask is displayed in Task Topology.

  • 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 size of used tablespace of the destination database is larger than that of the source database.

  • We recommend that you do not use gh-ost or pt-online-schema-change to perform DDL operations on objects to be synchronized. Otherwise, data synchronization may fail.

  • 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.

Billing

Synchronization typeTask configuration fee
Schema synchronization and full data synchronizationFree of charge.
Incremental data synchronizationCharged. For more information, see Billing overview.

Supported synchronization topologies

  • One-way one-to-one synchronization

  • One-way one-to-many synchronization

  • One-way cascade synchronization

  • One-way many-to-one synchronization

For more information, see Synchronization topologies.

SQL operations that can be synchronized

Operation type

SQL statement

DML

INSERT, UPDATE, and DELETE

DDL

ADD COLUMN

Permissions required for database accounts

Database

Required permission

References

Source PolarDB-X 1.0 instance

Read permissions on the objects to be synchronized.

Manage accounts

Procedure

  1. 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
  2. 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.
  3. Click Create Task. On the page that appears, configure the source and destination databases.

    Section

    Parameter

    Description

    N/A

    Task Name

    The name of the task. DTS automatically assigns a name to the task. 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 an existing DMS database instance

    The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements.

    • If you select an existing instance, DTS automatically populates the parameters for the database.

    • If you do not select an existing instance, you must manually configure parameters for the database.

    Database Type

    The type of the source database. Select PolarDB-X 1.0.

    Access Method

    The access method of the source database. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the source PolarDB-X 1.0 instance resides.

    Replicate Data Across Alibaba Cloud Accounts

    Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, No is selected.

    Instance ID

    The ID of the source PolarDB-X 1.0 instance.

    Database Account

    The database account of the source PolarDB-X 1.0 instance. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.

    Database Password

    The password of the database account.

    Destination Database

    Select an existing DMS database instance

    The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements.

    • If you select an existing instance, DTS automatically populates the parameters for the database.

    • If you do not select an existing instance, you must manually configure parameters for the database.

    Database Type

    The type of the destination database. Select DataHub.

    Access Method

    The access method of the destination database. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the destination DataHub project resides.

    Project

    The name of the destination DataHub project.

  4. In the lower part of the page, click Test Connectivity and Proceed.

    If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. 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 must ensure that the ECS instance can 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. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

    Warning

    If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the 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.

  5. Configure objects to synchronize and advanced settings.

    • Basic Settings

      Parameter

      Description

      Synchronization Type

      By default, Incremental Data Synchronization is selected. You can select only Schema Synchronization. You cannot select Full Data Synchronization.

      Note

      During initial schema synchronization, DTS synchronizes the schemas of the selected objects such as tables from the source database to the destination DataHub instance.

      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, only some columns are synchronized, or the data synchronization task fails. Operate with caution.

      Naming Rules of Additional Columns

      During data synchronization to a DataHub project, DTS adds additional columns to the destination topic. If the names of additional columns are the same as those of existing columns in the destination topic, data synchronization fails. You can set the Naming Rules of Additional Columns parameter to New Rule or Previous Rule based on your business requirements.

      Warning

      Before you set this parameter to Yes or No, check whether additional columns and existing columns in the destination topic have name conflicts. For more information, see Modify the naming rules for additional columns.

      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 Rightwards arrow icon to add the objects to the Selected Objects section.

      Note

      You can select tables as the objects to be synchronized.

      If you select an entire database as the object to be synchronized, DTS does not synchronize the changes made to create tables in or delete tables from the source database to the destination database.

      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 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, see Use SQL conditions to filter data.

    • 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:

      Specify the retry time range 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 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 your 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:
  6. Click Next: Save Task Settings and Precheck in the lower part of the page.

    You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.

    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 troubleshoot the issues based on the causes, 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 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.

  7. Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

  8. 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.

    Resource Group

    The resource group on which the instance is run. Default value: default resource group. For more information, see What is Resource Management?.

    Instance Class

    DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification 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, one year, two years, three years, or five years.

    Note

    This parameter is available only if you select the Subscription billing method.

  9. Read and select the check box to agree to the Data Transmission Service (Pay-as-you-go) Service Terms.

  10. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.