Synchronize data from an ODP logical table to a DataHub instance

This topic describes how to use OceanBase Migration Service (OMS) to synchronize data from a logical table of OceanBase Database Proxy (ODP) to a DataHub instance.

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.

• 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 and do not contain special characters. The special characters are line breaks, spaces, and the following characters: . | " ' ` ( ) = ; / & \.

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 task, some data (transmitted within the last minute) may be duplicated in the DataHub instance. Therefore, deduplication is required in downstream systems.

• If you select only Incremental Synchronization when you create a data synchronization task, OMS requires that the local incremental logs in the source database be retained for more than 48 hours.

  ​If you select Full Synchronization and Incremental Synchronization when you create the data synchronization task, OMS requires that the local incremental logs of the source database be retained for at least seven days. Otherwise, the data synchronization task may fail or the data in the source and target databases may be inconsistent because OMS cannot obtain incremental logs.

Supported DDL operations for synchronization

• ALTER TABLE

• CREATE INDEX

• DROP INDEX

• TRUNCATE

Procedure

1. Create a data synchronization task.

   

   1. Log in to the OMS console.

   2. In the left-side navigation pane, click Data Synchronization.

   3. On the Data Synchronization page, click Create Task in the upper-right corner.

2. On the Create Task page, specify the name of the synchronization task.

   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.

   Notice

   The task name must be a unique identifier in the OMS system.

3. On the Select Source and Target page, configure the parameters.

   

   Parameter	Description
   Source	If you have created an ODP 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 ODP data source.
   Target	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 the parameters, see Create a DataHub data source.
   Tag (Optional)	Click the field and select a tag from the drop-down list. You can also click Manage Tags to create, modify, and delete tags. For more information, see Use tags to manage data synchronization tasks.

4. Click Next. In the Select Synchronization Type step, specify the synchronization types for the current data synchronization task.

   The supported synchronization types are Schema synchronization, Full Synchronization, and Incremental Synchronization. Schema synchronization creates a topic. Full Synchronization does not support null uk or no uk. Incremental Synchronization supports the DML synchronization and DDL synchronization options, but does not support not null uk or null uk without sharding columns. The supported DML operations are INSERT, DELETE, and UPDATE. Select the options based on your business needs. For more information, see Configure DDL/DML synchronization.

   Notice

   If you select DDL Synchronization here, you can select only topics of the BLOB type on the Select Synchronization Objects page.

5. Click Next. In the Select Synchronization Objects step, select the target topic type and objects.

   Available topic types are Tuple and BLOB. Tuple topics do not support DDL synchronization but 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:

   1. In the left-side pane, select the objects to be synchronized.

   2. Click >.

   3. In the Map Object to Topic dialog box, select a mapping method.

      • To synchronize one Tuple table or one or more BLOB tables, select the required mapping method and click OK in the Map Object to Topic dialog box.

        If you did not select Schema synchronization as the synchronization type, you can select only Existed Topic here. If you have selected Schema synchronization when you specify the synchronization type, you can select only one mapping method to create or select a topic.

        For example, if you have selected Schema Synchronization, when you use both the Create Topic and Select Topic mapping methods or rename the topic, a precheck error will be returned due to option conflicts.

        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 Existed Topic 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 in the DataHub instance. By default, the number of data shards is 2 and the data validity period is 7 days. These parameters cannot be modified. If the topics do not meet your business needs, you can create topics in the target database as needed.

      • To synchronize multiple Tuple tables, click OK in the dialog box that appears.

        

        If you have selected a Tuple topic and multiple tables without selecting Schema synchronization, you must select an existing topic and click OK in the Map Object to Topic dialog box.

        

   4. Click OK.

   OMS allows you to import objects by using text, set row filtering, sharding columns, and column filtering for target objects, as well as remove a single object or all objects. Objects in the target database are listed in the structure of Topic > Database > Table.

   Operation	Description
   Import objects	In the list on the right, click Import Objects in the upper-right corner. In the dialog box that appears, click OK. Caution This operation will overwrite previous selections. Proceed with caution. In the Import Synchronization Objects dialog box, import the objects to be synchronized. You can import CSV files to configure synchronization objects. For more information, see Download and import the settings of synchronization objects. Click Validate. After the validation succeeds, click OK.
   Change topics	When the topic type is set to BLOB, you can change the topic for objects in the target database. For more information, see Change the topic.
   Configure settings	OMS allows you to use the WHERE clause to set row filters and select sharding columns and columns to synchronize. In the list on the right, move the pointer over the object that you want to set. Click Settings. In the Settings dialog box, you can perform the following operations: In the Row Filters section, specify a standard SQL WHERE clause to filter data by row. For more information, see Use SQL conditions to filter data. Select the sharding columns that you want to use from the Sharding Columns drop-down list. You can select multiple columns 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 columns 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 target 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. In the Select Columns section, select the columns to be synchronized. For more information, see Column filtering. Click OK.
   Remove one or all objects	OMS allows you to remove a single object or all objects to be synchronized to the target database during data mapping. Remove a single synchronization object In the list on the right, move the pointer over the object that you want to remove, and click Remove to remove the synchronization object. Remove all synchronization objects In the list on the right, click Remove All in the upper-right corner. In the dialog box that appears, click OK to remove all synchronization objects.

6. Click Next. In the Synchronization Options step, configure the parameters.

   • Full synchronization

     The following parameters are displayed only if you have selected Full Synchronization in the Select Synchronization Type step.

     Parameter	Description
     Full Synchronization Rate Limit	You can choose whether to limit the full synchronization rate as needed. If you choose to limit the full synchronization rate, you must specify the records per second (RPS) and bytes per second (BPS). The RPS specifies the maximum number of data rows synchronized to the target database per second during full synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target database per second during full synchronization. Note The RPS and BPS values specified here are only for throttling. The actual full synchronization performance is subject to factors such as the settings of the source and target databases and the instance specifications.
     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. By setting the resource configuration for the Full-Import component, you can limit the resource consumption of a task in the full synchronization stage. Notice In the case of custom configurations, the minimum value is 1, and only integers are supported.

   • Incremental synchronization

     The following parameters are displayed only if you have selected Incremental Synchronization in the Select Synchronization Type step.

     Parameter	Description
     Incremental Synchronization Rate Limit	You can choose whether to limit the incremental synchronization rate as needed. If you choose to limit the incremental synchronization rate, you must specify the RPS and BPS. The RPS specifies the maximum number of data rows synchronized to the target database per second during incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the target database per second during incremental synchronization. Note The RPS and BPS values specified here are only for throttling. The actual incremental synchronization performance is subject to factors such as the settings of the source and target databases and the instance specifications.
     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. By setting the resource configuration for the Store component, you can limit the resource consumption of a task in log pull in the incremental synchronization stage. 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 writes. By setting the resource configuration for the Incr-Sync component, you can limit the resource consumption of a task in data writes in the incremental synchronization stage. 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 task startup time and cannot be modified. If you did not select Full Synchronization as the synchronization type, set this parameter to a certain point in 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, DefaultExtendColumnType, Debezium, DebeziumFlatten, and DebeziumSmt. 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. At present, only MySQL-compatible tenants of OceanBase Database support Debezium, DebeziumFlatten, and DebeziumSmt.
     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 in the Select Synchronization Type step, the partitioning rule can be set only to Table.
     Business System Identification (Optional)	The identifier that identifies the source business system of data. This parameter is displayed only when Serialization Method is set to DataWorks. 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 task or component template.

   

7. Click Precheck.

   If an error is returned during the precheck, you can perform the following operations:

   • Identify and troubleshoot the problem and then perform the precheck again.

   • Click Skip in the Actions column of a failed precheck item. In the dialog box that prompts the consequences of the operation, click OK.

8. Click Start Task. If you do not need to start the task now, click Save to go to the details page of the task. You can start the task later as needed.

   OMS allows you to modify the synchronization objects when the data synchronization task is running. For more information, see View and modify synchronization objects. After the data synchronization task is started, it will be executed based on the selected synchronization types. For more information, see the View synchronization details section in View details of a data synchronization task.