Data Transmission Service:Synchronize data from a self-managed Oracle database to a MaxCompute project

Source database requirements

• Tables must have a primary key or unique key, with all fields unique. Without this, duplicate rows may appear in the destination.

• Oracle 12c and later: table names cannot exceed 30 bytes.

• If you rename tables or columns at the destination (Selected Objects > right-click), a single task supports up to 1,000 tables. For larger workloads, split tables across multiple tasks or synchronize the entire database without renaming.

• Oracle Real Application Cluster (RAC): use a virtual IP address (VIP), not a Single Client Access Name (SCAN) IP address. After you specify the VIP, node failover is not supported.

• If the Oracle RAC database connects over Express Connect, specify a VIP when configuring the task.

Log retention requirements

The redo logs and archived logs must meet the following minimum retention periods:

If logs are purged before DTS can read them, the task fails. In edge cases, data inconsistency or loss may occur. After full data synchronization completes, you can reduce the retention period to 24 hours.

Other limitations

• Do not perform a primary/secondary switchover while the task is running — the task will fail.

• Empty VARCHAR2 strings (treated as NULL by Oracle) cause failures if the corresponding destination column has a NOT NULL constraint.

• Tables with the Fine-Grained Audit (FGA) policy enabled: DTS cannot read the ORA_ROWSCN pseudocolumn and the task fails. Disable the FGA policy on affected tables, or exclude them from synchronization.

• Do not update LONGTEXT fields while synchronization is running.

• Do not run DDL operations during schema synchronization or initial full data synchronization.

• Do not use Oracle Data Pump to write to the source database during incremental data synchronization — data loss may occur.

• External tables cannot be synchronized.

• MaxCompute does not support primary key constraints. If network errors occur during synchronization, DTS may write duplicate rows to MaxCompute.

• Write to the destination MaxCompute project only through DTS to prevent data inconsistency.

• If DTS needs to recover a failed instance, the process may take up to 8 hours and may involve restarting the instance or adjusting DTS instance parameters (database parameters are not modified). For the parameters that may be changed, see Modify instance parameters.

Performance considerations

• Synchronize data during off-peak hours. Full data synchronization consumes read and write resources on both the source and destination databases.

• After full data synchronization, the destination tablespace may be larger than the source due to fragmentation from concurrent INSERT operations.

• Synchronization latency is calculated from the timestamp of the latest synchronized record in the destination versus the current timestamp in the source. If no DML operations run on the source for an extended period, the latency reading may be inaccurate. Run a DML operation on the source to refresh it, or enable a heartbeat table if you synchronize an entire database.

Step 1: Open the Data Synchronization page

Use one of the following consoles to start:

Step 2: Configure source and destination databases

Click Create Task to open the task configuration page. Configure the parameters as follows:

Step 3: Test connectivity

At the bottom of the page, click Test Connectivity and Proceed. In the CIDR Blocks of DTS Servers dialog box, click Test Connectivity.

Click OK to grant permissions to your MaxCompute account, then click Test Connectivity and Proceed.

Step 4: Configure objects to synchronize

In the Configure Objects step, set the following parameters:

Parameter	Description
Synchronization Types	Incremental Data Synchronization is selected by default. Also select Schema Synchronization and Full Data Synchronization to run all three phases.
Naming Rules of Additional Columns	DTS adds extra columns to destination tables. If an additional column name conflicts with an existing column, the task fails and data loss can occur. Select New Rule or Previous Rule based on your requirements. Check for naming conflicts before setting this parameter. See Naming rules for additional columns.
Partition Definition of Incremental Data Table	Select partition names based on your requirements. See Partition.
Processing Mode of Conflicting Tables	Precheck and Report Errors (default): checks for identical table names in source and destination. The precheck fails if conflicts exist. To resolve conflicts, use the object name mapping feature to rename destination tables. See Map object names. Ignore Errors and Proceed: skips the conflict check. During full synchronization, existing destination records are kept; during incremental synchronization, existing records are overwritten. If schemas differ, initialization may fail or only some columns may be synchronized.
Capitalization of Object Names in Destination Instance	Controls the case of database, table, and column names in the destination. Default: DTS default policy. See Specify the capitalization of object names in the destination instance.
Source Objects	Select one or more tables and click to add them to Selected Objects. Only tables can be synchronized.
Selected Objects	To rename a single object: right-click it and specify a new name. See Map the name of a single object. To rename multiple objects: click Batch Edit. See Map multiple object names at a time. To filter rows: right-click the table and set filter conditions. See Specify filter conditions. Renaming an object may cause other objects that depend on it to fail synchronization.

Step 5: Configure advanced settings

Click Next: Advanced Settings and configure the following:

Step 6: Run the precheck

Click Next: Save Task Settings and Precheck.

DTS runs a precheck before the task can start. If the precheck fails:

• Click View Details next to each failed item, resolve the issue, and click Precheck Again.

• For alert items that can be ignored: click Confirm Alert Details, then Ignore in the dialog, then OK, then Precheck Again. Ignored alerts may result in data inconsistency.

Step 7: Purchase a data synchronization instance

1. Wait until Success Rate reaches 100%, then click Next: Purchase Instance.

2. On the buy page, configure the following:

   Section	Parameter	Description
   New Instance Class	Billing Method	Subscription: pay upfront for a fixed term — more cost-effective for long-term use. Pay-as-you-go: billed hourly — suitable for short-term use. Release the instance when no longer needed to stop charges.
   	Resource Group Settings	The resource group for the instance. Default: default resource group. See What is Resource Management?
   	Instance Class	The synchronization throughput class. See Instance classes of data synchronization instances.
   	Subscription Duration	Available for the Subscription billing method. Options: 1–9 months, 1 year, 2 years, 3 years, or 5 years.

3. Read and accept Data Transmission Service (Pay-as-you-go) Service Terms.

4. Click Buy and Start, then click OK in the confirmation dialog.

The task appears in the task list. Monitor its progress from the list.