This topic describes how to synchronize data from an Db2 for LUW database to an AnalyticDB for MySQL V3.0 cluster by using Data Transmission Service (DTS).

Prerequisites

  • The source Db2 for LUW database and the destination AnalyticDB for MySQL V3.0 cluster are created. For more information about the supported database versions, see Overview of data synchronization scenarios.
  • The available storage space of the destination database is larger than the total size of the data in the source database.

Limits

Note By default, DTS disables FOREIGN KEY constraints for the destination database in a data synchronization task. Therefore, the cascade and delete operations of the source database are not synchronized to the destination database.
Category Description
Limits on the source database
  • Bandwidth requirements: The server to which the source database belongs must have a sufficient egress bandwidth. Otherwise, the data synchronization speed is affected.
  • 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 edit tables (such as renaming tables or columns) in the destination database, up to 1,000 tables can be synchronized 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 split the tables and configure multiple tasks to synchronize the tables, or configure a task to synchronize the entire database.
  • The following requirements for data logs must be met:
    • The data logging feature must be enabled. Otherwise, error messages are returned during precheck and the data synchronization task cannot be started.
    • If you perform only incremental data synchronization, the data logs of the source database must be stored for more than 24 hours. If you perform both full data synchronization and incremental data synchronization, the data logs of the source database must be stored for at least seven days. After the full data synchronization is completed, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the data logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of data logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability and performance.

Other limits
  • Schema synchronization is not supported. Before you configure a data synchronization task, you must create databases and tables in the destination instance.
  • DTS synchronizes incremental data from a Db2 for LUW database to the destination database based on the Change Data Capture (CDC) replication technology of Db2 for LUW. However, the CDC replication technology has its own limits. For more information, see General data restrictions for SQL Replication.
  • 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 full data synchronization, DTS uses read and write resources of the source and destination databases. This may cause the loads of the database servers to increase.
  • During full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is completed, 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. Otherwise, data synchronization may fail.
  • If you use only DTS to write data to the destination database, you can use Data Management (DMS) to perform online DDL operations on the source tables. For more information, see Change schemas without locking tables.
  • 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.
  • AnalyticDB for MySQL V3.0 has limits on the usage of disk space. If the disk space usage of the nodes in an AnalyticDB for MySQL V3.0 cluster reaches 80%, the DTS task is delayed and error messages are returned. We recommend that you estimate the required disk space based on the objects to be synchronized. You must ensure that the destination cluster has sufficient storage space.
  • AnalyticDB for MySQL V3.0 has strictly case-sensitive data.
Special cases You must take note of the following items because the source Db2 for LUW database is a self-managed database:
  • 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 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 be synchronized, you can create a heartbeat table. The heartbeat table is updated or receives data every second.

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 statements
DML INSERT, UPDATE, and DELETE

Before you begin

Procedure

  1. Go to the Data Synchronization Tasks page.
    1. Log on to the DMS console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
  2. On the right side of Data Synchronization Tasks, select the region where the data synchronization instance resides.
    Note If you use the new DTS console, you must select the region where 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 task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to use a unique task name.

    Source Database Database Type Select DB2 for LUW.
    Access Method Select Express Connect, VPN Gateway, or Smart Access Gateway.
    Instance Region Select the region where the Db2 for LUW database resides.
    Replicate Data Across Alibaba Cloud Accounts In this example, select No because data is replicated within the same Alibaba Cloud account.
    Peer VPC Select the ID of the virtual private cloud (VPC) that is connected to the Db2 for LUW database.
    IP Address Enter the server IP address of the Db2 for LUW database.
    Port Number Enter the service port number of the Db2 for LUW database. The default port number is 50000.
    Database Name Enter the name of the source Db2 for LUW database.
    Database Account Enter the account of the Db2 for LUW database. For information about the permissions that are required for the account, see Before you begin.
    Database Password

    The password of the database account.

    Destination Database Database Type Select AnalyticDB MySQL V3.0.
    Access Method Select Cloud Instance.
    Instance Region Select the region where the destination AnalyticDB for MySQL V3.0 cluster resides.
    Instance ID Select the ID of the destination AnalyticDB for MySQL V3.0 cluster.
    Database Account Enter the database account of the destination PolarDB-X V2.0 cluster. For information about the permissions that are required for the account, see Before you begin.
    Database Password

    The password of the database account.

  4. In the lower part of the page, click Test Connectivity and Proceed.
    Note
    • You do not need to modify the security settings for ApsaraDB instances (such as ApsaraDB RDS for MySQL and ApsaraDB for MongoDB) and ECS-hosted databases. DTS automatically adds the CIDR blocks of DTS servers to the whitelists of ApsaraDB instances or the security group rules of ECS instances. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
    • After data synchronization is complete, we recommend that you remove the CIDR blocks of DTS servers from the whitelists or security groups.
  5. Select the objects to migrate.
    • Basic Settings
      Parameter Description
      Task Stages

      Incremental Data Synchronization is selected by default. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is completed, DTS synchronizes the historical data of selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization.

      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 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 migrated 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 schema, and a data record has the same primary key 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, initial data synchronization may fail. In this case, only part of the columns are synchronized, or the data synchronization task fails.
      DDL and DML Operations to Be Synchronized

      Select the DDL and DML operations that you want to synchronize. For more information, see SQL operations that can be synchronized.

      Note To select the SQL operations performed on a specific database or table, perform the following steps: In the Selected Objects section, right-click an object. In the dialog box that appears, select the SQL operations that you want to synchronize.
      Merge Tables
      • Yes: In online transaction processing (OLTP) scenarios, sharding is implemented to speed up the response to business tables. In online analytical processing (OLAP) scenarios, you can store a large amount of data in a single table. It makes your SQL queries more efficient. This way, you can merge multiple source tables that have an identical schema into a single destination table. This feature allows you to synchronize data from multiple tables in the source database to a single table in the destination database.
        Note
        • After you select multiple tables from the source database, you must change the names of these tables to the name of the destination table by using the object name mapping feature. For more information about how to use this feature, see Map object names.
        • DTS adds a column named __dts_data_source to the destination table. This column is used to record the data source. The data type of this column is TEXT. The values of this column are in the following format: data synchronization instance ID:source database name:source schema name:source table name. This allows DTS to identify each source table. Example: dts********:dtstestdata:testschema:customer1.
        • If you set this parameter to Yes, all the selected source tables in the task are merged into a destination table. If you want to merge only part of the source tables, you must create a separate data synchronization task for these tables.
        Warning We recommend that you do not perform DDL operations to change the schemas of source databases or tables. Otherwise, data inconsistency may occur or the migration task fails.
      • No: the default value.
      Capitalization of Object Names in Destination Instance

      Specifies the capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that of 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 columns, tables, or databases as objects to synchronize. If you select tables or columns as the objects to synchronize, DTS does not synchronize other objects such as views, triggers, and stored procedures to the destination database.
      Selected Objects
      • To rename an object in 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 in the destination instance, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time.
    • Advanced Settings
      Parameter Description
      Set Alerts
      Specifies whether to set alerts for the data synchronization task. If you select yes, DTS sends notifications to contacts if the task fails or the synchronization latency exceeds the upper limit.
      • No: does not set alerts.
      • Yes: sets alerts. In this case, you must also set the alert threshold and alert contacts.
      Retry Time for Failed Connection
      Specifies the retry time range for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time range to more than 30 minutes. 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 an instance serves as the source or destination database of multiple data synchronization tasks, the less value that is specified for the instance 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 needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
      Configure ETL
      Specify whether you want to enable the ETL feature. For more information, see What is ETL?.
      • If you select Yes, the ETL feature is enabled. You must specify a policy in the text box.
      • If you select No, the ETL feature is disabled.
  6. In the lower part of the page, click Next: Configure Database and Table Fields. On the page that appears, set the primary key column and distribution key column of the tables that you want to synchronize to the destination AnalyticDB for MySQL cluster.
    AnalyticDB for MySQL: Specify the primary key columns and distribution keys
    Note If you select Schema Synchronization for the synchronization type, you must specify the type, primary key column, and distribution key for the tables that you want to synchronize to the AnalyticDB for MySQL V3.0 cluster. For more information, see CREATE TABLE.
  7. 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 task fails to pass the precheck, you can click the Info icon icon next to each failed item to view details.
      • After you troubleshoot the issues based on the causes, you can run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  8. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  9. On the Purchase Instance page, specify the billing method and specifications for the data synchronization instance. The following table describes related parameters.
    Section Parameter Description
    Parameters Billing method
    • Subscription: You pay for your subscription 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 billed on an hourly basis. For short-term use, we recommend that you select the pay-as-you-go billing method. If you no longer need a pay-as-you-go instance, you can release the instance to reduce costs.
    Instance Class DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class based on your business scenario. For more information, see Specifications of data synchronization instances.
    Subscription Duration If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months or one to three years.
    Note This parameter is available only if you select the subscription billing method.
  10. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  11. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.