This topic describes how to synchronize data from an IDB logical table to a DataHub instance in the OceanBase Migration Service (OMS) console.
Limitations
DDL synchronization applies only to BLOB topics.
The name of a table to be synchronized, as well as the names of columns in the table, must not contain Chinese characters.
The IDB must have a primary key logical table so that it can be synchronized to a DataHub instance.
Data source identifiers and user accounts must be globally unique in OMS.
OMS supports the synchronization of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are . | " ' ` ( ) = ; / & \n
Considerations
If the clocks between nodes or between the client and the server are out of synchronization, the latency may be inaccurate during incremental synchronization.
For example, if the clock is earlier than the standard time, the latency can be negative. If the clock is later than the standard time, the latency can be positive.
When data transmission is resumed for a project, some data (transmitted within the last minute) may be duplicated in the DataHub instance. Therefore, data deduplication is required in downstream applications.
Supported DDL
ALTER TABLECREATE INDEXDROP INDEXTRUNCATE
Procedure
Create a data synchronization project.
Log on to the OMS console.
In the left-side navigation pane, click Data Synchronization.
On the Data Synchronization page, click Create Synchronization Project in the upper-right corner.
On the Select Source and Destination page, configure the parameters.
Parameter Description Synchronization Project Name We recommend that you set it to a combination of digits and letters. It must not contain any spaces and cannot exceed 64 characters in length. Tag (Optional) Click the field and select a target tag from the drop-down list. You can also click Manage Tags to create, modify, and delete tags. For more information, see Manage data synchronization projects by using tags. Source If you have created an IDB data source, select it from the drop-down list. If not, click New Data Source in the drop-down list to create one in the dialog box on the right side. For more information, see Create an IDB data source. Destination If you have created a DataHub data source, select it from the drop-down list. If not, click New Data Source in the drop-down list to create one in the dialog box on the right side. For more information about parameters, see Create a DataHub data source. Click Next. On the Select Synchronization Type page, select the synchronization type for the current data synchronization project.
The supported synchronization types include Schema Synchronization, Full Synchronization, and Incremental Synchronization. Schema Synchronization creates a topic. Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. The supported DML operations are
Insert,Delete, andUpdate. Select the options based on your business needs. For more information, see DML filtering and DDL synchronization.Click Next. On the Select Synchronization Objects page, select the topic type and scope for synchronization.
Available topic types are Tuple and BLOB. Tuple topics support records similar to database records. Each record contains multiple columns. BLOB topics only support a binary block as a record. Data is Base64-encoded for transmission. For more information, visit the documentation center of DataHub.
After you select the topic type for synchronization, perform the following operations:
Enter the global unique ID (GUID) in the GUID field.
In the left-side pane, select the objects to be synchronized.
Click >.
Select a mapping method.
Notice
When you set the topic type to Tuple without selecting Schema Synchronization, you can only synchronize a single table to a single topic.
To synchronize a single table, select the mapping method as needed in the Map Object to Topic dialog box and click OK.
If you do not select Schema Synchronization when you specify the synchronization type, you can select only Existing Topics here.
Parameter Description Create Topic Enter the name of the new topic in the text box. The topic name can contain letters, digits, and underscores (_) and must start with a letter. It must not exceed 128 characters in length. Select Topic OMS allows you to query DataHub topics. You can click Select Topic, and then find and select a topic for synchronization from the Existing Topics drop-down list. You can also enter the name of an existing topic and select it after it appears. Batch Generate Topics The format for generating topics in batches is Topic_${Database Name}_${Table Name}.If you select Create Topic or Batch Generate Topics, after the schema migration succeeds, you can query the created topics on the DataHub side. By default, the number of data shards is 2 and the data expiration time is 7 days. These parameters cannot be modified. If the topics do not meet your business needs, you can create topics in the destination database as needed.
To synchronize multiple tables, click OK in the dialog box that appears.
After you select synchronization objects, you can change the topic, set sharding columns, and remove a single object or all objects. Objects in the destination database are listed in the structure of Topic > Database > Table.
Operation Description Change the topic When the topic type is set to BLOB, you can change the topic for objects in the destination. For more information, see Change the topic. Configure settings - In the list on the right, hover over the object that you want to set.
- Click Settings.
- In the Settings dialog box, click Shard Columns and select the target sharding columns in the drop-down list. You can select multiple fields as sharding columns. This parameter is optional.
Unless otherwise specified, select the primary key as sharding columns. If the primary key is not load-balanced, select load-balanced fields with unique identifiers as sharding columns to avoid potential performance issues. Sharding columns can be used for the following purposes:- Load balancing: Threads used for sending messages can be recognized based on the sharding columns if the destination table supports concurrent writes.
- Orderliness: OMS ensures that messages are received in order if the values of the sharding columns are the same. The orderliness specifies the sequence of executing DML statements for a column.
- Click OK.
Remove one or all objects During data mapping, OMS allows you to remove one or more selected objects to be migrated or synchronized to the destination. - Remove a single synchronization object
In the list on the right of the selection section, hover over the target object, and click Remove. The synchronization object is removed. - Remove all synchronization objects
In the list on the right of the selection section, click Remove All in the upper-right corner. In the dialog box that appears, click OK to remove all synchronization objects.
Click Next. On the Synchronization Options page, specify the following parameters.
Full synchronization
The following table describes the full synchronization parameters, which are displayed only when you have selected Full Synchronization on the Select Synchronization Type page.
Parameter Description Full Synchronization Resource Configuration You can select Small, Medium, or Large to use the corresponding default values of Read Concurrency, Write Concurrency, and Memory. You can also customize the resource configurations for full synchronization. Through resource configuration for the Full-Import component, you can limit the resource consumption of a project in the full synchronization phase. Notice
In the case of custom configurations, the minimum value is 1 and only integers are supported.
Incremental synchronization
The following table describes the incremental synchronization parameters, which are displayed only when you have selected Incremental Synchronization on the Select Synchronization Type page.
Parameter Description Incremental Log Pull Resource Configuration You can select Small, Medium, or Large to use the corresponding default value of Memory. You can also customize the resource configurations for incremental log pull. Through resource configuration for the Store component, you can limit the resource consumption of a project in log pull in the incremental synchronization phase. Notice
In the case of custom configurations, the minimum value is 1 and only integers are supported.
Incremental Data Write Resource Configuration You can select Small, Medium, or Large to use the corresponding default values of Write Concurrency and Memory. You can also customize the resource configurations for incremental data write. Through resource configuration for the Incr-Sync component, you can limit the resource consumption of a project in data writes in the incremental synchronization phase. Notice
In the case of custom configurations, the minimum value is 1 and only integers are supported.
Incremental Record Retention Time The duration that incremental parsed files are cached in OMS. A longer retention period results in more disk space occupied by the Store component. Incremental Synchronization Start Timestamp - If you have selected Full Synchronization as the synchronization type, the default value of this parameter is the project startup time and cannot be modified.
- If you do not select Full Synchronization as the synchronization type, set this parameter to a certain point of time, which is the current system time by default. For more information, see Set an incremental synchronization timestamp.
Advanced options
Parameter Description Serialization Method The message format for synchronizing data to a DataHub instance. Valid values: Default, Canal, Dataworks (version 2.0 supported), SharePlex, and DefaultExtendColumnType. For more information, see Data formats.
Notice
This parameter is available only when the topic type is set to BLOB on the Select Synchronization Type page.Partitioning Rules The rule for synchronizing data from the source database to a DataHub topic. Valid values: Hash and Table. We recommend that you select Table to ensure DDL and DML consumption consistency when downstream applications are consuming messages. - Hash indicates that OMS uses a hash algorithm to select the shard of a DataHub topic based on the value of the primary key or sharding column.
- Table indicates that OMS delivers all data in a table to the same partition and uses the table name as the hash key.
Notice
If you select DDL Synchronization on the Select Synchronization Type page, the partitioning rule can be set only to Table.
Business System Identification (Optional) Identifies the source business system of data. The business system identifier consists of 1 to 20 characters.
If the parameter settings on the page cannot meet your requirements, you can click Parameter Configuration in the lower part of the page to configure more specific settings. You can also reference an existing project or component template.
Click Precheck.
Take note of the following items if an error is returned during the precheck:
You can identify and troubleshoot the error and then perform the precheck again.
You can also click Skip in the Actions column of a failed precheck item. In the dialog box that appears, you can view the prompt for the consequences of the operation and click OK.
Click Start Project. If you do not need to start the project now, click Save to go to the details page of the data synchronization project. You can start the project later as needed.
OMS allows you to modify the synchronization objects when the data synchronization project is running. For more information, see View and modify synchronization objects. After a data synchronization project is started, the synchronization objects will be executed based on the selected synchronization type. For more information, see the "View synchronization details" section in the View details of a data synchronization project topic.
If the data synchronization project encounters a running exception due to a network failure or slow startup of processes, you can click Recover on the Synchronization Projects page or on the Details page of the synchronization project.