Synchronize data from an OceanBase database to a RocketMQ instance

Message Queue for Apache RocketMQ is a distributed message-oriented middleware built by Alibaba Cloud based on Apache RocketMQ. It features low latency, high concurrency, and high reliability. The data synchronization feature of OceanBase Migration Service (OMS) allows you to synchronize data between an OceanBase physical table and a RocketMQ data source in real time, extending the message processing capability.

For more information about the data formats for the two types of tenants, see Data formats.

Prerequisites

• You have created a dedicated database user for data synchronization in the source OceanBase database, and granted corresponding privileges to the users. For more information, see Create a database user.

• You have created data sources for the source and destination. For more information, see Create a physical OceanBase data source and Create a RocketMQ data source.

Limits

• OMS Enterprise Edition and Community Edition support RocketMQ 4.x and 5.x instances.

• Only physical tables can be synchronized.

• During data synchronization, OMS allows you to drop a table before creating a new one. In other words, you can execute DROP TABLE and then execute CREATE TABLE. In OMS, you cannot create a new table by renaming a table. That is, you cannot execute RENAME TABLE a TO a_tmp.

• 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, user accounts, and tags must be globally unique in OMS.

• OMS supports only the synchronization of objects whose database name or table name is an ASCII string without special characters. The special characters are . | \ " ' ` ( ) = ; / & \n

Usage notes

• When data transmission is resumed for a project, some data (transmitted within the last minute) may be duplicated in the RocketMQ instance. Therefore, data deduplication is required in downstream applications.

• If the clocks are not synchronized between the nodes or between the client and a server, the latency of incremental synchronization may be negative.

• We recommend that you select no more than 15,000 database objects for a project.

  If a table contains LOB fields or contains more than 500 columns, we recommend that you create a dedicated project for the table and set the JVM parameters of related components as needed. For example, set the limitator.select.batch.max parameter for the full verification component, the sourceBatchSize parameter for the full import component, and the sourceBatchSize parameter for the incremental synchronization component.

  Execute the following statement to query tables that contain LOB fields: SELECT DISTINCT(TABLE_NAME) FROM ALL_TAB_COLUMNS WHERE DATA_TYPE IN ('BLOB', 'CLOB', 'NCLOB') AND OWNER = XXX;.

Procedure

1. Create a data synchronization project.

   1. Log on to the OMS console.

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

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

2. On the Select Source and Destination page, specify the following 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.
   Labels	Click the field and select a target tag from the drop-down list. You can 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 a physical OceanBase data source, select it from the drop-down list. Otherwise, click Add Data Source in the drop-down list to create one in the dialog box on the right side. For more information, see Create a physical data source of OceanBase Database. Notice The source database cannot be an instance of OceanBase Database V4.0.0.
   Destination	If you have created a RocketMQ data source, select it from the drop-down list. Otherwise, click Add Data Source in the drop-down list to create one in the dialog box on the right side. For more information, see Create a RocketMQ data source.

3. Click Next. On the Select Synchronization Type page, select the synchronization type for the current data synchronization project.

   Options for Synchronization Type are Full Synchronization and Incremental Synchronization. Incremental Synchronization supports only the DML Synchronization option. The supported DML operations are Insert, Delete, and Update. Select the options based on your business needs. For more information, see DML filtering.

4. (Optional) Click Next.

   If the source database is an OceanBase database, you must configure the obconfig_url parameter, username, and password for incremental synchronization.

   If you have selected Incremental Synchronization without configuring the required parameters for the source database, the More About Data Sources dialog box appears to prompt you to configure the parameters. For more information, see Create a physical OceanBase data source.

   After you configure the parameters, click Test Connectivity. After the test succeeds, click Save.

5. Click Next. On the Select Synchronization Objects page, select a synchronization scope.

   When you synchronize data from an OceanBase database to a RocketMQ instance, you can select multiple tables to map to multiple topics.

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

   2. Click >.

   3. Click the Existing Topics drop-down list in the Map the Object to the Topic dialog box and select the target topic.

      You can also enter the name of an existing topic and select it after it appears.

   4. Click OK.

   OMS allows you to import objects from text files, change the topics of the objects, set row-based filtering, or remove a single object or all objects. Objects in the destination database are listed in the structure of Topic > Database > Table.

   Actions	Steps
   Import Objects	In the list on the right, click Import Objects in the upper-right corner. In the dialog box that appears, click OK. Notice 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 rename databases/tables and set row filtering conditions. For more information, see Download and import the settings of synchronization objects. Click Validate. After the validation succeeds, click OK.
   Change Topic	In the list on the right, move the pointer over the target object. Click Change Topic. In the Map Object to Topic dialog box, change the topics to be synchronized. Click OK. Notice The selected topics and tables will be merged into the selected topic. Proceed with caution.
   Parameter	OMS allows you to configure row-based filtering, select sharding columns, and select columns to be synchronized. In the list on the right, move the pointer over the target object. 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 fields as sharding columns. This parameter is optional. Unless otherwise specified, select the primary keys as sharding columns. If the primary keys are not load-balanced, select fields with unique identifiers and whose load is balanced 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. In the Select Columns section, select the columns to be synchronized. For more information, see Column filtering. Click OK.
   Remove/Remove All	During data mapping, OMS allows you to remove one or more selected objects to be migrated to the destination. Remove a single synchronization object In the list on the right of the selection section, move the pointer 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.

6. Click Next. On the Synchronization Options page, specify the following parameters.

   Parameter	Description
   Incremental Synchronization Start Timestamp	This parameter specifies to synchronize data after the synchronization start timestamp. The default value is the current system time. You can select a point in time or enter a timestamp. Notice You can select the current time or a point in time earlier than the current time. This parameter is closely related to the retention period of archived logs. Generally, you can start data synchronization from the current timestamp.
   Serialization Method	The message format for synchronizing data to a RocketMQ instance. Valid values: Default, Canal, Dataworks (version 2.0 supported), SharePlex, DefaultExtendColumnType, and Debezium. For more information, see Data formats. Notice At present, MySQL tenants of OceanBase Database supports only Debezium.
   Enable Intra-Transaction Sequence	Specifies whether to maintain order within a transaction. If this feature is enabled, OMS marks the sequence number for a transaction to be sent to a downstream node. Notice This parameter is valid only for the SharePlex format and is intended for you to obtain the sequence numbers of the DML statements that form a transaction. For example, if a transaction contains 10 DML statements numbered from 1 to 10, OMS will deliver data to the destination database in the same order.
   Partitioning Rule	When you synchronize data to a RocketMQ instance, only Hash is supported. Hash indicates that OMS uses a hash algorithm to select the message queue (MQ) for RocketMQ based on the value of the primary key or sharding column.
   Business System Identification (Optional)	Identifies the source business system of data. The business system identifier consists of 1 to 20 characters.
   Enter the name of the producer group	This parameter specifies a producer group that can write data into multiple topics.
   Whether to Allow Message Tracing	This parameter specifies whether to allow message tracing. If message tracing is enabled, you can trace the entire project information of a message in the procedure from sending the message to the RocketMQ server to message consumption, including node time and status. The message tracing feature provides data support for troubleshooting in the production environment.

7. Click Precheck.

   During the precheck, OMS detects the connection with the destination data source. If an error is returned during the precheck:

   • You can identify and troubleshoot the issue and then perform the precheck again.

   • You can click Skip in the Actions column of the precheck item with the error. A dialog box will be displayed, prompting the impact caused if you skip this error. If you want to continue, click OK in the dialog box.

8. 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 data access fails due to a network failure or the slow startup of processes, go to the project list or the project details page and click Restore.