OceanBase MySQL to DataHub Replication

Use this page to replicate OceanBase MySQL data to DataHub in NineData. It supports schema replication, full replication, and incremental replication.

Before you begin

• Add the source and target data sources to NineData. For details, see Add Data Source.
• The source database type is OceanBase MySQL.
• The target data source type is DataHub.

Limitations

• Check the performance of both data sources before you start. Run replication during off-peak hours so full initialization does not overload the source or target.
• Make sure each synchronized table has a primary key or unique constraint, and keep column names unique to avoid duplicate rows.

Procedure

1. Sign in to the NineData Console.

2. In the left navigation pane, click Replication > Data Replication.

3. On the Replication page, click Create Replication.

4. On the Source & Target tab, configure the fields in the table, and click Next.

   Parameter	Description
   Name	Enter a name for the data synchronization task. To make the task easier to find and manage later, use a meaningful name. Up to 64 characters are supported.
   Source	The data source that contains the objects to synchronize.
   Datahub Project	Select the target Datahub Project. Data from the source data source will be written to the specified Project.
   Type	Select the replication type. Schema: Synchronize only the database and table schemas of the source data source, without synchronizing data. Full: Synchronize all objects and data from the source data source, namely full data replication. The switch on the right enables periodic full replication. For more information, see Periodic Full Replication. Incremental: After full synchronization is complete, perform incremental synchronization based on the logs of the source data source.The icon is used to configure incremental operation types. You can clear specific operation types as needed. Cleared operation types will be ignored during incremental synchronization.
   Incremental Started	Required only when Type is Incremental. From Started: Use the current replication task start time as the baseline for incremental replication. Customized Time: Select the point in time from which incremental replication starts. You can select a time zone based on the region of your business. If the configured time point is earlier than the current replication task start time and DDL operations occurred during that period, the replication task will fail.
   Spec (Unavailable only when Schema is selected)	The specification of the replication task. A larger specification provides a higher replication rate. Hover over the icon to view the rate and configuration information of each specification. Each specification shows the available quantity and total quantity. When the available quantity is 0, the specification is grayed out and cannot be selected.
   If target table already exists (Required when Schema is selected)	Pre-Check Error and Stop Task: Stop the task when a table with the same name is detected during the precheck stage. Skip and Continue Task: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, ignore the table with the same name. If you also perform data replication, data is appended to the table with the same name and existing data is not overwritten. Delete Objects and Rewrite: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, delete the table with the same name in the target database and replicate the table schema again based on the source database. If you also perform data replication, data is written after schema replication is complete.
   Target Table Exists Data (Required when Full is selected)	Pre-Check Error and Stop Task: Stop the task when data is detected in the target table during the precheck stage. Ignore existing target data and append to it.: When data is detected in the target table during the precheck stage, ignore that data and append other data. Clear target existing data before write: When data is detected in the target table during the precheck stage, delete that data and write it again.
   Incremental data conflict handling strategy for target table (Required when Incremental is selected)	Runtime error: During incremental replication, report an error when target data already exists and wait for manual intervention. Do not update target data: During incremental replication, do not write data when target data already exists, and continue subsequent tasks. Update target data: During incremental replication, overwrite the target data when target data already exists.

5. On the Objects tab, configure the parameters in the table, and click Next.

   Parameter	Description

   To create multiple replication tasks with the same replication objects, import a configuration file. Click Import Config, click Download Template to download the template, edit the file, and then click Upload to upload it and import the objects in bulk. The configuration file uses these fields:

   Parameter	Description
   source_table_name	The source table name of the object to synchronize.
   destination_table_name	The target table name that receives the synchronized object.
   source_schema_name	The source schema name of the object to synchronize.
   destination_schema_name	The target schema name that receives the synchronized object.
   source_database_name	The source database name of the object to synchronize.
   target_database_name	The target database name that receives the synchronized object.
   column_list	The list of columns to synchronize.
   extra_configuration	Additional configuration information. This field supports: column_rules: Defines column mappings and value rules. Field descriptions: column_name: Original column name. destination_column_name: Specifies the target column name. column_value: Specifies the column value, which can be an SQL function or a constant value. filter_condition: Specifies row-level data filtering conditions. Only rows that meet the conditions are replicated.

   tip

   • Example of extra_configuration:

     {
       "extra_config":{
         "column_rules":[
           {
              "column_name": "created_time",
              "destination_column_name": "migrated_time",
              "column_value": "current_timestamp()"
           }
         ],
          "filter_condition": "id != 0"
       }
     }

     In this example, created_time is mapped to migrated_time, the target column value is changed to current_timestamp(), and only rows whose id value is not 0 are synchronized.

   • For a complete example of the configuration file, see the downloaded template.

6. On the "Mapping" tab, configure mapping based on the selected replication type, and click Save and Pre-Check.

   • Includes Schema: Configure the table name after synchronization to the target data source.

   • Does not include Schema: The system selects the database with the same name in the target data source by default. If no such database exists, select the target database manually. The table names and column names in the target database must match the synchronization objects. If they do not match, map the table names and column names manually.

   You can also perform these actions:

   • If source or target metadata changes while you configure mappings, click Refresh Metadata to refresh the metadata.

   • Click Column selection and processing configuration to the right of the target table to configure each column separately.

   • Click Column selection and processing configuration to the right of the target table to configure System Field Configuration. Datahub is a queue product and does not support random UPDATE or DELETE operations. Therefore, NineData adds the following metadata fields to the user's Datahub to identify the characteristics of each record delivered to Datahub.

     Metadata Field Name	Metadata Field Value
     _record_id_	${nd_record_id}
     _operation_type_	${nd_operation_type}
     _execution_time_	${nd_exec_timestamp}
     _before_image_	${nd_before_image}
     _after_image_	${nd_after_image}

     You can also add or modify metadata field names or values as needed. For details about the values of each field, see the Appendix in this topic.

   • Click Column selection and processing configuration for the target table to configure Data Filter by using comparison expressions. Only rows that match the filtering conditions are replicated to the target data source. For example, if the filtering condition is emp_no>=10005, rows whose emp_no value is less than 10005 are not replicated.

7. On the "Pre-check" tab, wait for the system to complete the precheck. After the precheck passes, click Launch.

   • Select Enable data consistency comparison to start a data consistency comparison task based on the source data source after synchronization completes. Based on the selected Type, Enable data consistency comparison starts at these times:

     • Schema: Starts after schema replication is complete.
     • Schema+Full: Starts after full replication is complete.
     • Full: Starts after full replication is complete.
     • Schema+Full+Incremental, Incremental: Starts when incremental data is consistent with the source data source for the first time and Delay is 0 seconds. Click View Details to view synchronization delay on the Details page.

   • If the precheck fails, click Details in the Actions column for the failed check item, review the cause, fix the issue, and then click Check Again to run the precheck again until it passes.

   • Items with Warning in Result can be fixed or ignored as needed.

8. On the Launch page, the Launch Successfully message appears, indicating that the synchronization task has started. You can then perform these actions:

   • Click View Details to view the execution status of each stage of the synchronization task.
   • Click Back to list to return to the Replication task list page.

Results

1. Sign in to the NineData Console.

2. In the navigation menu, click Replication > Data Replication.

3. On the Replication page, click the Task ID of the target synchronization task. The task details page shows the following information.

   

   Number	Function	Description
   1	Sync Delay	The synchronization delay between the source and target data sources. 0 seconds means the target has caught up with the source, so you can switch traffic based on your migration plan.
   2	Configure Alerts	When the task fails, the system notifies the selected channel through the configured alert.
   3	More	Pause: Pause the task. Only tasks with Running status are selectable. Duplicate: Create a new replication task with the same configuration as the current task. Terminate: Terminate tasks that are incomplete or still listening (that is, in incremental synchronization). After a task is terminated, it cannot be restarted, so proceed with caution. If the synchronization objects contain triggers, trigger replication options appear for selection. Delete: Delete the task. Once deleted, it cannot be recovered, so proceed with caution.
   4	Structure Replication (displayed in scenarios involving structure replication)	Displays the progress and detailed information of structure replication. Click Log to view the execution logs of structure replication. Click the to view the latest information. Click View DDL in the Actions column for the target object in the list to view SQL replay.
   5	Full Replication (displayed in scenarios involving full replication)	Displays the progress and detailed information of full replication. Click Monitor to view various monitoring indicators during full replication. During full replication, you can also click Flow Control Settings on the monitoring page to limit the rate of writing to the target data source per second. The unit is rows/second. Click Log to view the execution logs of full replication. Click the to view the latest information.
   6	Incremental Replication (displayed in scenarios involving incremental replication)	Displays incremental replication indicators. Click View Threads to view the operations currently being executed by the current replication task, including: Thread ID: Replication tasks are executed in multiple threads, and this shows the current thread number. Execute SQL: Details of the SQL statement currently being executed by the current thread. Response Time: The response time of the current thread. If this value increases, it indicates that the current thread may be stuck for some reason. Event Time: The timestamp when the current thread was started. Status: The status of the current thread. Click Flow Control Settings to limit the rate of writing to the target data source per second. The unit is rows/second. Click Log to view the execution logs of incremental replication. Click the to view the latest information.
   7	Modify Object	Displays the modification records of synchronization objects. Click Modify Objects to configure the synchronization objects. Click the to view the latest information.
   8	Data Comparison	Displays the comparison results between the source and target data sources. If data comparison is not enabled, click Enable Comparison on the page to enable it. Click Re-compare to rerun the comparison for the current source and target data sources. Click Stop to stop the comparison task immediately after it starts. Click Log to view the execution logs of consistency comparison. Click Monitor (displayed only in data comparison) to view the trend chart of RPS (records per second) comparison. Click Details to view earlier records. Click the in the Actions column in the comparison list (displayed under the Data tab only when inconsistencies are found) to view details of the comparison between the source and target data sources. Click the in the Actions column in the comparison list (displayed only when inconsistencies are found): Generate change SQL. You can copy this SQL to the target data source and run it to fix the mismatch.
   9	Expand	Displays detailed information of the current replication task. Common actions: Export table configuration: Export the current task's database and table configuration so you can quickly import it when creating another replication task with the same objects. Alert Rules: Configure alerts for the current task.

Appendix: Data type mapping

Type	OceanBase MySQL Data Type	DataHub Default Mapping Data Type
Numeric Types	BOOL, BOOLEAN	BOOLEAN
	TINYINT	TINYINT
	SMALLINT	SMALLINT
	MEDIUMINT	MEDIUMINT
	INT	INT
	BIGINT	BIGINT
	DECIMAL, DOUBLE	DECIMAL
	FLOAT	FLOAT
	DOUBLE	DOUBLE
	BIT	STRING
Date Types	DATETIME (without time zone), TIMESTAMP (with time zone)	TIMESTAMP
	DATE	STRING
	TIME	STRING
	YEAR	INT
Character Types	CHAR (up to 256), VARCHAR (up to 262144), BINARY (up to 256), VARBINARY (up to 1048576), ENUM, SET	STRING
Large Objects	TINYBLOB (up to 255), BLOB (up to 65535), MEDIUMBLOB (up to 16777215), LARGEBLOB (up to 536870910), TINYTEXT (up to 255), TEXT (up to 65535), MEDIUMTEXT (up to 16777215), LARGETEXT (up to 536870910)	STRING
JSON Type	JSON	STRING
Spatial Types	GEOMETRY, POINT, LINESTRING, POLYGON, MULTIPOINT, MULTISTRING, MULTIPOLYGON, GEOMETRYCOLLECTION	STRING

Appendix: Pre-check items

Check Item	Check Content
Source Data Source Check	Checks the source data source gateway status, instance reachability, and username/password validity.
Target Data Source Check	Checks the target data source gateway status, instance reachability, and username/password validity.
Source Database Permission Check	Checks whether the source database account permissions meet the requirements.
Target Database Data Existence Check	Checks whether data already exists for the objects to be replicated in the target database.

Appendix: System parameters

To store incremental data in DataHub, NineData provides default metadata fields that identify data characteristics. The following table describes these parameters and when to use them.

Parameter Name	Meaning and Usage
${nd_record_id}	The unique ID for each data record (Record). In UPDATE operations, the record_id must remain the same before and after the update to achieve change association.
${nd_exec_timestamp}	The execution time of the Record operation.
${nd_database_name}	The name of the database to which the table belongs, facilitating data source differentiation.
${nd_table_name}	The name of the table corresponding to the Record, used for precise location of change records.
${nd_operation_type}	The type of Record change operation, with the following values: I: Insert U: Update D: Delete For full synchronization, all are I.
${nd_before_image}	The before-image identifier, indicating that the target Record status is before the change occurs, i.e., the current data has been changed. Values: Y: Before-image. N: Not a before-image. For example: INSERT operation is N; DELETE operation is Y; UPDATE operation before is Y, after is N.
${nd_after_image}	The after-image identifier, indicating that the target Record status is after the change occurs, i.e., the current data is the latest state. Values: Y: After-image. N: Not an after-image. For example: INSERT operation is Y; DELETE operation is N; UPDATE operation before is N, after is Y.
${nd_datasource}	Data source information: The IP and port number of the data source, in the format ip:port.

Related documents

Data Replication Introduction