Synchronize data from Db2 for LUW to PolarDB for MySQL - Data Transmission Service

Prerequisites

The source Db2 for LUW database and the destination PolarDB for MySQL cluster are created. For supported versions, see Synchronization solution overview.
The destination database must have more storage space than the source database.

Usage notes

Note

During schema synchronization, DTS synchronizes foreign keys from the source database to the destination database.
During full data synchronization and incremental data synchronization, DTS temporarily disables constraint checks and foreign key cascade operations at the session level. Data inconsistency may occur if cascade update or delete operations are performed on the source database while the task is running.

Limit type	Description
Limits on the source database	The server that hosts the source database must have sufficient outbound bandwidth. Otherwise, the data synchronization speed decreases. 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 modify the tables in the destination database, such as renaming tables or columns, you can synchronize up to 5,000 tables in a single task. If you synchronize more than 5,000 tables, a request error occurs. In this case, we recommend that you split the tables across multiple tasks or synchronize the entire database. The data logging feature must be enabled. Otherwise, error messages are returned during precheck, and the data synchronization task cannot be started. Note If you perform only incremental data synchronization, the data logs of the source database must be retained for more than 24 hours. If you perform both full and incremental data synchronization, the data logs must be retained for at least seven days. Otherwise, DTS may fail to obtain the data logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. 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 based on these requirements. Otherwise, the service reliability or performance stated in the SLA of DTS cannot be guaranteed. Do not run DDL operations that change database or table schemas during schema synchronization or full synchronization. Otherwise, the synchronization task fails. Note During full synchronization, DTS queries the source database. This creates metadata locks that may block DDL operations on the source database.
Other limits	DTS synchronizes incremental data from a Db2 for LUW database to the destination database based on the CDC replication technology of Db2 for LUW. The CDC replication technology has its own limits. For more information, see General data restrictions for SQL Replication. Evaluate the impact of data synchronization on the performance of the source and destination databases before you start. We recommend that you synchronize data during off-peak hours. During initial full data synchronization, DTS uses read and write resources of the source and destination databases, which may increase the load on the database servers. During initial full data synchronization, concurrent INSERT operations cause fragmentation in the destination tables. After full data synchronization is complete, the used tablespace of the destination database is larger than that of the source database. If your data includes four-byte characters—such as rare Chinese characters or emojis—the destination database and table must use the utf8mb4 charset. Note If you use DTS to synchronize table schemas, set the `character_set_server` parameter at the instance level in the destination database to utf8mb4. During data synchronization, we recommend that you use only DTS to write data to the destination database to prevent data inconsistency. After data synchronization is complete, you can use DMS to execute DDL statements online. For more information, see Perform lock-free DDL operations. If DDL statements fail in the destination database, the data synchronization task continues to run. You can view the failed DDL statements in the task logs. For more information, see View task logs. If you write columns with names that differ only in case to the same table in the destination MySQL database, unexpected results may occur because MySQL column names are case-insensitive. After data synchronization completes (the instance's Status is Completed), you should use the `ANALYZE TABLE <table_name>` command to confirm that all data is written to the target table. For example, after the HA failover mechanism is triggered in the target MySQL database, data might be written only to memory, which can cause data loss. If a task fails, DTS support staff will attempt to restore it within eight hours. During restoration, they may restart the task or adjust its parameters. Note Only DTS task parameters are modified—not database parameters. Parameters that may be adjusted include those listed in Modify instance parameters.
Special cases	The source Db2 for LUW database is a self-managed database. When you synchronize data from the Db2 for LUW database, note the following items: If you perform a primary/secondary switchover on the source database while the data synchronization task is running, the task fails. DTS calculates synchronization latency based on the timestamp of the latest synchronized data record 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 synchronization latency 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.

Billing

Synchronization type	Pricing
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. 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.

Supported SQL operations

Operation type	SQL operation
DML	INSERT, UPDATE, and DELETE

Preparations

Create database accounts and grant permissions to them.

Database	Required permissions	Authorization method
Db2 for LUW	DBADM authority	See Creating a user and Authorities overview
Destination PolarDB for MySQL cluster	Read and write permissions on the destination database	Create and manage a database account

Enable the log archiving feature for the Db2 for LUW database. For more information, see logarchmeth1 - Primary log archive method configuration parameter and logarchmeth2 - Secondary log archive method configuration parameter.

Procedure

Go to the data synchronization task list page in the destination region. You can do this in one of two ways.
DTS console
1. Log on to the DTS console.
2. In the navigation pane on the left, click Data Synchronization.
3. In the upper-left corner of the page, select the region where the synchronization instance is located.
DMS console
Note
The actual steps may vary depending on the mode and layout of the DMS console. For more information, see Simple mode console and Customize DMS console layout and style.
1. Log on to the DMS console.
2. In the top menu bar, choose Data + AI > DTS (DTS) > Data Synchronization.
3. To the right of Data Synchronization Tasks, select the region of the synchronization instance.
Click Create Task to open the task configuration page.
Optional: In the upper-right corner of the page, click New Configuration Page.
Note
- If you are already on the new configuration page (the button in the upper-right corner is Back to Previous Version), you can skip this step.
- Some parameters differ between the new and old configuration pages. We recommend using the new version.

Configure the source and destination databases.

Section	Parameter	Description
N/A	Task Name	DTS automatically generates a task name. We recommend that you specify a descriptive name for easy identification. The name does not need to be unique.
Source Database	Database Type	Select DB2 for LUW.
	Connection Type	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	Select No to synchronize data within the same account.
	The VPC that has been connected to the source database	Select the VPC ID to which the Db2 for LUW database is connected.
	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. Default: 50000.
	Database Name	Enter the name of the source database that contains the objects to synchronize.
	Database Account	Enter the database account of the Db2 for LUW instance. For required permissions, see Preparations.
	Database Password	Enter the password for the specified database account.
Destination Database	Database Type	Select PolarDB for MySQL.
	Connection Type	Select Alibaba Cloud Instance.
	Instance Region	Select the region where the destination PolarDB for MySQL cluster resides.
	PolarDB Cluster ID	Select the ID of the destination PolarDB for MySQL cluster.
	Database Account	Enter the database account of the destination PolarDB for MySQL instance. For required permissions, see Preparations.
	Database Password	Enter the password for the specified database account.
	Encryption	Select an option based on your requirements. For more information, see Configure SSL encryption.

After the configuration is complete, click Test Connectivity and Proceed at the bottom of the page. In the CIDR Blocks of DTS Servers dialog box, click Test Connectivity.
Note
Ensure that the IP address blocks of the DTS service are added to the security settings of the source and destination databases, either automatically or manually, to allow access from DTS servers. For more information, see Add the IP address whitelist of DTS servers.

Configure the task objects.

On the Configure Objects page, specify the objects to synchronize.

Parameter	Description
Synchronization Type	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.
Processing Mode for Existing Destination Tables	Precheck and Report Errors: Checks for tables with the same names in the destination database. If any tables with the same names are found, an error is reported during the precheck and the data synchronization task does not start. Otherwise, the precheck is successful. Note If you cannot delete or rename the table with the same name in the destination database, you can map it to a different name in the destination. For more information, see Object name mapping. Ignore Errors and Proceed: Skips the check for tables with the same name in the destination database. Warning Selecting Ignore Errors and Proceed may cause data inconsistency and put your business at risk. For example: If the table schemas are consistent and a record in the destination database has the same primary key or unique key value as a record in the source database: During full data synchronization, DTS retains the destination record and skips the source record. During incremental synchronization, DTS overwrites the destination record with the source record. If the table schemas are inconsistent, data initialization may fail. This can result in only partial data synchronization or a complete synchronization failure. Use with caution.
Case Policy for Destination Object Names	Configure the case-sensitivity policy for database, table, and column names in the destination instance. By default, the DTS default policy is selected. You can also choose to use the default policy of the source or destination database. For more information, see Case policy for destination object names.
Source Objects	In the Source Objects box, click the objects, and then click to move them to the Selected Objects box. Note You can select objects at the database, table, or column level. If you select only tables or columns, DTS does not synchronize other object types (such as views, triggers, and stored procedures).
Selected Objects	To rename a single object in the destination instance, right-click the object in the Selected Objects box. For more information, see Map a single object name. To rename multiple objects in bulk, click Batch Edit in the upper-right corner of the Selected Objects box. For more information, see Map multiple object names in bulk. Note Object name mapping may cause data inconsistency or synchronization failure for dependent objects. For example, column mapping with partial table synchronization or inconsistent table schemas may result in data loss for missing columns. To filter data by using a WHERE clause, right-click the table in the Selected Objects section and set the filter conditions. For instructions, see Set filter conditions. To select SQL operations for incremental synchronization at the database or table level, right-click the object in the Selected Objects section and select the SQL operations in the dialog box.

Click Next: Advanced Settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS uses a shared cluster for tasks, so you do not need to make a selection. For greater task stability, you can purchase a dedicated cluster to run the DTS synchronization task. For more information, see What is a DTS dedicated cluster?.
Select the engine type of the destination database	Select the storage engine for the destination database. InnoDB: the default storage engine. X-Engine: an OLTP database storage engine.
Retry Time for Failed Connections	If the connection to the source or destination database fails after the synchronization task starts, DTS reports an error and immediately begins to retry the connection. The default retry duration is 720 minutes. You can customize the retry time to a value from 10 to 1,440 minutes. We recommend a duration of 30 minutes or more. If the connection is restored within this period, the task resumes automatically. Otherwise, the task fails. Note If multiple DTS instances (e.g., Instance A and B) share a source or destination, DTS uses the shortest configured retry duration (e.g., 30 minutes for A, 60 for B, so 30 minutes is used) for all instances. DTS charges for task runtime during connection retries. Set a custom duration based on your business needs, or release the DTS instance promptly after you release the source/destination instances.
Retry Time for Other Issues	If a non-connection issue (e.g., a DDL or DML execution error) occurs, DTS reports an error and immediately retries the operation. The default retry duration is 10 minutes. You can also customize the retry time to a value from 1 to 1,440 minutes. We recommend a duration of 10 minutes or more. If the related operations succeed within the set retry time, the synchronization task automatically resumes. Otherwise, the task fails. Important The value of Retry Time for Other Issues must be less than that of Retry Time for Failed Connections.
Enable Throttling for Full Data Synchronization	During full data synchronization, DTS consumes read and write resources from the source and destination databases, which can increase their load. To mitigate pressure on the destination database, you can limit the migration rate by setting Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s). Note This parameter is available only if Synchronization Types is set to Full Data Synchronization. You can also adjust the rate of full data synchronization when the synchronization instance is running.
Enable Throttling for Incremental Data Synchronization	You can also limit the incremental synchronization rate to reduce pressure on the destination database by setting RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s).
Environment Tag	Select an environment tag to identify the instance. Optional in this example.
Configure ETL	Based on your business needs, select whether to configure the ETL feature to process data. Yes: Configures the ETL feature. You must also enter data processing statements in the text box. No: Does not configure the ETL feature.
Monitoring and Alerting	Choose whether to set up alerts. If the synchronization fails or the latency exceeds the specified threshold, DTS sends a notification to the alert contacts. No: No alerts are configured. Yes: Configures alerts. You must also set the alert threshold and alert notifications. For more information, see Configure monitoring and alerting during task configuration.

Click Data Verification to configure a data verification task.
To use the data verification feature, see Configure data verification.

Save the task and perform a precheck.
- To view the parameters for configuring this instance via an API operation, hover over the Next: Save Task Settings and Precheck button and click Preview OpenAPI parameters in the tooltip.
- If you have finished viewing the API parameters, click Next: Save Task Settings and Precheck at the bottom of the page.
Note
- Before a synchronization task starts, DTS performs a precheck. You can start the task only if the precheck passes.
- If the precheck fails, click View Details next to the failed item, fix the issue as prompted, and then rerun the precheck.
- If the precheck generates warnings:
  For non-ignorable warning, click View Details next to the item, fix the issue as prompted, and run the precheck again.
  For ignorable warnings, you can bypass them by clicking Confirm Alert Details, then Ignore, and then OK. Finally, click Precheck Again to skip the warning and run the precheck again. Ignoring precheck warnings may lead to data inconsistencies and other business risks. Proceed with caution.

Purchase the instance.

When the Success Rate reaches 100%, click Next: Purchase Instance.

On the Purchase page, select the billing method and link specifications for the data synchronization instance. For more information, see the following table.

Category	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay upfront for a specific duration. This is cost-effective for long-term, continuous tasks. Pay-as-you-go: You are billed hourly for actual usage. This is ideal for short-term or test tasks, as you can release the instance at any time to save costs.
	Resource Group Settings	The resource group to which the instance belongs. The default is default resource group. For more information, see What is resource management?.
	Instance Class	DTS offers synchronization specifications at different performance levels that affect the synchronization rate. Select a specification based on your business requirements. For more information, see Data synchronization link specifications.
	Subscription Duration	In subscription mode, select the duration and quantity of the instance. Monthly options range from 1 to 9 months. Yearly options include 1, 2, 3, or 5 years. Note This option appears only when the billing method is Subscription.

Read and select the checkbox for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start, and then click OK in the OK dialog box.
You can monitor the task progress on the data synchronization page.