Create a task to synchronize data from OceanBase Database Community Edition to a Kafka instance

Kafka is a widely used high-performance distributed stream computing platform. OceanBase Migration Service (OMS) Community Edition supports real-time data synchronization between OceanBase Database Community Edition and a self-managed Kafka instance, extending the message processing capability. Therefore, OMS Community Edition is widely applied to business scenarios such as real-time data warehouse building, data query, and report distribution.

OMS Community Edition enables you to synchronize data to message queue products, extending the all-around application of your business in big data fields, such as data aggregation monitoring, streaming data processing, and online/offline analysis. For more information about the data formats for OceanBase Database Community Edition, see Data formats.

Prerequisites

You have created a dedicated database user for data synchronization in the source OceanBase Database Community Edition and granted the required privileges to the user. For more information, see Create a database user.

Limitations

• Only physical tables can be synchronized.

• OMS Community Edition supports Kafka V0.9, V1.0, and V2.x.

  Notice

  When the version of the Kafka instance is 0.9, schema synchronization is not supported.

• During data synchronization, if you rename a source table to be synchronized and the new name is beyond the synchronization scope, the data of the source table will not be synchronized to the destination Kafka instance.

• The name of a table to be synchronized, as well as the names of columns in the table, must not contain Chinese characters.

• The data source identifiers and user accounts must be globally unique in OMS Community Edition.

• OMS Community Edition supports the synchronization of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are line breaks and | " ' ` ( ) = ; / &.

• The source cannot be a standby OceanBase database.

Considerations

• To ensure the performance of a data synchronization task, we recommend that you synchronize no more than 1,000 tables at a time.

• In a data synchronization task where the source is OceanBase Database Community Edition and DDL synchronization is enabled, if a RENAME operation is performed on a table in the source, we recommend that you restart the task to avoid data loss during incremental synchronization.

• During incremental synchronization from OceanBase Database V4.x, if the STORED attribute is not marked for a generated column, the column value synchronized to the destination is NULL. As a result, the data of this column received by the downstream system is not as expected.

• Take note of the following items when an updated row contains a LOB column:

  • If the LOB column is updated, do not use the value stored in the LOB column before the UPDATE or DELETE operation.

    The following data types are stored in LOB columns: JSON, GIS, XML, user-defined type (UDT), and TEXT such as LONGTEXT and MEDIUMTEXT.

  • If the LOB column is not updated, the value stored in the LOB column before and after the UPDATE or DELETE operation is NULL.

• 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 transfer is resumed for a task, some data (within the last minute) may be duplicated in the Kafka instance. Therefore, deduplication is required in downstream systems.

• During data synchronization from OceanBase Database Community Edition to a Kafka instance, if the execution of a statement to create a unique index fails in the source, the Kafka instance will consume the creation and deletion DDL statements. If the downstream DDL statement for unique index creation fails the execution, ignore this exception.

  Notice

  Liboblog V2.2.x does not guarantee the order of DDL or DML statements and may cause data quality issues.

Supported DDL

• CREATE TABLE

  Notice

  The created table must be a synchronization object. To execute the CREATE TABLE statement on a synchronized table, execute the DROP TABLE statement on this table first.

• ALTER TABLE

• DROP TABLE

• TRUNCATE TABLE

  In delayed deletion, the same transaction contains two identical TRUNCATE TABLE DDL statements. In this case, idempotence is implemented for downstream consumption.

• ALTER TABLE…TRUNCATE PARTITION

• CREATE INDEX

• DROP INDEX

• COMMENT ON TABLE

• RENAME TABLE

  Notice

  The renamed table must be a synchronization object.

Procedure

1. Create a data synchronization task.

   1. Log on to the console of OMS Community Edition.

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

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

2. On the Select Source and Destination page, configure the parameters.

   Parameter	Description
   Task 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 Use tags to manage data synchronization tasks.
   Source	If you have created a data source of OceanBase Database Community Edition, 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 data source of OceanBase Database Community Edition.
   Destination	If you have created a Kafka 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 a Kafka data source.

3. Click Next. On the Select Synchronization Type page, specify the synchronization types for the current data synchronization task.

   Valid values: Schema Synchronization, Full Synchronization, and Incremental Synchronization. Full Synchronization supports the synchronization of tables without primary keys. Incremental Synchronization supports DML Synchronization and DDL Synchronization.

4. (Optional) Click Next.

   To synchronize data from OceanBase Database Community Edition, you need to specify OCP (Optional), DRC User Name, and Password for schema migration and incremental synchronization.

   If you have selected Schema Migration and 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 about the parameters, see Create a data source of OceanBase Database Community Edition.

   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.

   You can use the Specify Objects or Match Rules option to specify synchronization objects. The following procedure describes how to specify synchronization objects by using the Specify Objects option. For information about the procedure for specifying synchronization objects by using the Match Rules option, see the "Configure matching rules for data migration/synchronization from a database to a Message Queue instance" section in the Configure matching rules topic.

   When you synchronize data from OceanBase Database Community Edition to a Kafka instance, you can synchronize data from multiple tables to multiple topics.

   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.

      If you did not select Schema Synchronization when you set the synchronization type, you can select only Existing Topics here. If you have selected Schema Synchronization when you set 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 contains 3 to 64 characters, and can contain only letters, digits, hyphens (-), underscores (_), and periods (.).
      Select Topic	OMS Community Edition allows you to query Kafka topics. You can click Select Topic, and then find and select the topics to be synchronized 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 in the Kafka instance. By default, the number of partitions is 3 and the number of partition replicas is 1. These parameters cannot be modified. If the topics do not meet your business needs, you can create topics in the destination database as needed.

   4. Click OK.

   When you synchronize data from OceanBase Database Community Edition to a Kafka instance, OMS Community Edition allows you to import objects from text and perform the following operations on the objects in the destination database: change topics, set row filtering conditions, and remove a single object or all objects. Objects in the destination 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. 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 migration objects 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 topics	OMS Community Edition allows you to change topics for objects in the destination. For more information, see Change topics.
   Configure settings	OMS Community Edition 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 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 fields as sharding columns. This parameter is optional. Unless otherwise specified, select the primary key as sharding columns. If the primary keys are 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 Community Edition 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 Community Edition allows you to remove a single object or all objects to be migrated to the destination database during data mapping. 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.

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

   Parameter	Description
   Incremental Synchronization Start Timestamp	If you select Full Synchronization as the synchronization type, the default value of this parameter is the task 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. 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 archive logs. Generally, you can start data synchronization from the current timestamp.
   Serialization Method	The message format for synchronizing data to the Kafka instance. Valid values: Default, Canal, Dataworks (V2.0), SharePlex, DefaultExtendColumnType, Debezium, DebeziumFlatten, Maxwell, and DebeziumSmt. For more information, see Data formats. Notice: Only MySQL tenants of OceanBase Database support Debezium, DebeziumFlatten, and DebeziumSmt. If the message format is set to Dataworks, DDL operations COMMENT ON TABLE and ALTER TABLE…TRUNCATE PARTITION cannot be synchronized.
   Partitioning Rules	The rule for synchronizing data from an OceanBase database to a Kafka topic. OMS Community Edition supports Hash, Table, and One. For more information about the delivery of DDL statements in different scenarios and examples, see the description below. Hash indicates that OMS Community Edition uses a hash algorithm to select the partition of a Kafka topic based on a hashed value of the value of the primary key or sharding column. Table indicates that OMS Community Edition delivers all data in a table to the same partition and uses the table name as the hash key. One indicates that JSON messages are delivered to a partition under a topic to ensure ordering.
   Business System Identification (Optional)	Identifies the source business system of data. The business system identifier consists of 1 to 20 characters.

   The following table describes the delivery of a DDL statement in different scenarios.

   Partitioning Rules	When the DDL statement involves multiple tables (example: RENAME TABLE)	When the DDL statement involves unknown tables (example: DROP INDEX)	When the DDL statement involves a single table
   Hash	The DDL statement is delivered to all partitions of the topics associated with the involved tables. Assume that the DDL statement involves three tables, A, B, and C. If A is associated with Topic 1, B is associated with Topic 2, and C is not involved in the current task, the DDL statement is delivered to all partitions of Topic 1 and Topic 2.	The DDL statement is delivered to all partitions of all topics of the current task. Assume that the DDL statement cannot be identified by OMS Community Edition. If the current task has three topics, the DDL statement is delivered to all partitions of these three topics.	The DDL statement is delivered to all partitions of the topic associated with the table.
   Table	The DDL statement is delivered to specific partitions of the topics associated with the tables. The partitions correspond to the hash values of the names of involved tables. Assume that the DDL statement involves three tables, A, B, and C. If A is associated with Topic 1, B is associated with Topic 2, and C is not involved in the current task, the DDL statement is delivered to specific partitions corresponding to the hash values of the involved table names in Topic 1 and Topic 2.	The DDL statement is delivered to all partitions of all topics of the current task. Assume that the DDL statement cannot be identified by OMS Community Edition. If the current task has three topics, the DDL statement is delivered to all partitions of these three topics.	The DDL statement is delivered to a partition of the topic associated with the table.
   One	The DDL statement is delivered to a fixed partition of the topics associated with the tables. Assume that the DDL statement involves three tables, A, B, and C. If A is associated with Topic 1, B is associated with Topic 2, and C is not involved in the current task, the DDL statement is delivered to a fixed partition of Topic 1 and Topic 2.	The DDL statement is delivered to a fixed partition of all topics of the current task. Assume that the DDL statement cannot be identified by OMS Community Edition. If the current task has three topics, the DDL statement is delivered to a fixed partition of these three topics.	The DDL statement is delivered to a fixed partition of the topic associated with the table.

7. Click Precheck.

   During the precheck, OMS Community Edition detects the connection with the destination Kafka instance. 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 the 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 data synchronization task. You can start the task later as needed.

   OMS Community Edition 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 the View details of a data synchronization task topic.

   If the data synchronization task encounters an execution exception due to a network failure or slow startup of processes, you can click Recover on the Synchronization Tasks or Details page of the synchronization task.