ApsaraDB for OceanBase:Synchronize data from OceanBase Database to a DataHub instance

Prerequisites

• The data transmission service has the privilege to access cloud resources. For more information, see Grant privileges to roles for data transmission.

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

Limitations

• When you select full synchronization, data transmission supports only tables with unique keys.

• DDL synchronization applies only to BLOB topics.

• During data synchronization, the data transmission service allows you to drop a table before creating a new one. In other words, you can execute DROP TABLE and then execute CREATE TABLE. The data transmission service does not allow you to create a new table by renaming a table. In other words, you cannot execute RENAME TABLE a TO a_tmp.

• The data transmission service supports synchronization of data of the UTF8 and GBK character sets.

• 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 transmission service supports the synchronization of an object only when the following conditions are met: the database name, table name, and column name of the object are ASCII-encoded without special characters. The special characters are line breaks, spaces, and the following characters: . | " ' ` ( ) = ; / & \.

• The data transmission service does not support a standby OceanBase database as the source.

DataHub has the following limitations:

DataHub limits the size of a message based on the cloud environment. Usually, a message can be up to 1 MB in size. DataHub sends messages in batches, with each batch sized no more than 4 MB.

Considerations

• In a data synchronization task where the source is an OceanBase database and DDL synchronization is enabled, if a RENAME operation is performed on a table in the source database, 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 specified for a generated column, the values of this column synchronized to the destination become NULL for a Tuple topic. For a BLOB topic, this column will not be synchronized to the destination.

• 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 you select only Incremental Synchronization when you create a data synchronization task, the data transmission service requires that the local incremental logs in the source database be retained for at least 48 hours.

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

• When you synchronize incremental data from an OceanBase database to a DataHub instance, the MySQL schema is synchronized to the DataHub schema and then initialized. The following table lists the data types supported by DataHub. These data types apply only to Tuple topics.

  Type	Description	Value range
  BIGINT	An 8-byte signed integer.	-9223372036854775807 ~ 9223372036854775807
  DOUBLE	An 8-byte double-precision floating-point number.	-1.0 _10^308 ~ 1.0 _10^308
  BOOLEAN	A boolean value.	True/False true/false 0/1
  TIMESTAMP	A timestamp.	It is accurate to microseconds.
  STRING	A string that supports only UTF-8 encoding.	A single STRING column supports a maximum of 2 MB.
  INTEGER	A 4-byte integer.	-2147483648 ~ 2147483647
  FLOAT	A 4-byte single-precision floating-point number.	-3.40292347_10^38 ~ 3.40292347_10^38
  DECIMAL	A digital value.	- 10^38 +1 ~ 10^38 - 1

Supported source and destination instance types

In the following table, OB_MySQL stands for a MySQL tenant of OceanBase Database, and OB_Oracle stands for an Oracle tenant of OceanBase Database.

Supported DDL

• ALTER TABLE

  • ADD COLUMN

  • MODIFY COLUMN

  • DROP COLUMN

• CREATE INDEX

• DROP INDEX

• TRUNCATE TABLE

  Note

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

Data type mappings

A task that synchronizes data to a DataHub instance supports only the following data types: INTEGER, BIGINT, TIMESTAMP, FLOAT, DOUBLE, DECIMAL, STRING, and BOOLEAN.

• If you create a topic of another type when you set topic mapping, data synchronization will fail.

• The following table describes the default mapping rules, which are the most appropriate. If you change the mapping, an error may occur.

Supplemental properties

If you manually create a topic, add the following properties to the DataHub schema before you start a data synchronization task. If the data transmission service automatically creates a topic and synchronizes the schema, the data transmission service automatically adds the following properties.

Procedure

1. Log on to the ApsaraDB for OceanBase console and purchase a data synchronization task.

   For more information, see Purchase a data synchronization task.

2. Choose Data Transmission > Data Synchronization. On the page that appears, click Configuration for the data synchronization task.

   

   If you want to reference the configurations of an existing task, click Reference Configuration. For more information, see Reference and clear the configuration of a data synchronization task.

3. 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 an OceanBase data source, select it from the drop-down list. If not, click New Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information about the parameters, see Create an OceanBase data source. Important The source must not be an OceanBase Database tenant instance.
   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 and create one in the dialog box that appears on the right. For more information about the parameters, see Create a DataHub data source.

4. Click Next. On the Select Synchronization Type page, 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. Options for Incremental Synchronization are DML Synchronization and DDL Synchronization. The supported DML operations are INSERT, DELETE, and UPDATE. You can select operations as needed. For more information, see Configure DDL/DML synchronization.

   Note

   If you select DDL Synchronization, you can select only BLOB as the topic type on the Select Synchronization Objects page.

   

5. Click Next. On the Select Synchronization Objects page, select the topic type and objects to be synchronized in the current data synchronization task.

   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, you can select Specify Objects or Match Rules to specify the 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.

   Note

   If you selected DDL Synchronization in the Select Synchronization Type step, we recommend that you select synchronization objects by using the Match Rules option. This ensures that all new objects meeting the matching rules are synchronized. If you selected synchronization objects by using the Specify Objects option, new or renamed objects will not be synchronized.

   1. In the Select Synchronization Objects section, select Specify Objects.

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

   3. Click >.

   4. Select a mapping method.

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

        

        If you have not selected Schema Synchronization as the synchronization type, you can select only Existing Topics. 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	The data transmission service allows you to query DataHub topics. You can click Select Topic, and then find and select the topics to be synchronized from the Existing Topics drop-down list.
        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, you can query the newly created topics in the DataHub instance after schema synchronization is completed. By default, each DataHub topic has two partitions and the data expiration period is 7 days, which cannot be modified.

      • 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.

        

        In this case, multiple tables are displayed under the topic in the right pane, but only one table can be synchronized. Then, click Next. A prompt appears, indicating that only one-to-one mapping is supported between Tuple topics and tables.

        

   The data transmission service allows you to import objects by using text. It also allows you to rename objects, set row filters, and remove a single object or all objects. Objects in the destination database are listed in the structure of Topic > Database > Table.

   Note

   When you select Match Rules to specify synchronization objects, object renaming is implemented based on the syntax of the specified matching rules. In the operation area, you can only set filtering conditions and select sharding columns and the columns to be synchronized. For more information, see Configure matching rules.

   

   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. Important 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 or 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 topics	When the topic type is set to BLOB, you can change topics for objects in the destination database. For more information, see Change topics.
   Configure settings	The data transmission service allows you to filter data by row by using WHERE clauses, select sharding columns, and select the columns to be synchronized. In the list on the right, move the pointer over the table 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 keys 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: The data transmission service 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	The data transmission service allows you to remove a single object or all migration objects that are added to the right-side list 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. On the Synchronization Options page, configure the parameters.

   • Full synchronization

     The following table describes the parameters for full synchronization, which are displayed only if you have selected Full Synchronization on the Select Synchronization Type page.

     

     Parameter	Description
     Read Concurrency Configuration	The concurrency for reading data from the source during full synchronization. The maximum value is 512. A high concurrency may incur excessive stress on the source, thereby affecting the business.
     Write Concurrency Configuration	The concurrency for writing data to the destination during full synchronization. The maximum value is 512. A high write concurrency may incur excessive stress on the destination, affecting the business.
     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 destination per second during full synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the destination 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 destination and the instance specifications.

   • 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
     Write Concurrency Configuration	The concurrency for writing data to the destination during incremental synchronization. The maximum value is 512. A high write concurrency may incur excessive stress on the destination, affecting the business.
     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 destination per second during incremental synchronization, and the BPS specifies the maximum amount of data in bytes synchronized to the destination 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 destination and the instance specifications.
     Incremental Synchronization Start Timestamp	This parameter will not be displayed if you have selected Full Synchronization. If you have selected Incremental Synchronization but not Full Synchronization, specify a point in time after which data is to be synchronized. The default value is the current system time. For more information, see Set an incremental synchronization timestamp.

   • Advanced parameters

     

     Parameter	Description
     Serialization Method	The message format for synchronizing data to the destination DataHub instance. Valid values include Default, Canal, DataWorks (version 2.0 supported), SharePlex, DefaultExtendColumnType, Debezium, DebeziumFlatten, and DebeziumSmt. For more information, see Data formats used in serialization methods. Important This parameter is available only if you have set the topic type to BLOB on the Select Synchronization Objects page. Only MySQL 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 the data transmission service 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 the data transmission service delivers all data in a table to the same partition and uses the table name as the hash key. Note If you have selected 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. This parameter is displayed only when you select DataWorks for Serialization Method. The business system identifier consists of 1 to 20 characters.

7. Click Precheck.

   During the precheck, the data transmission service checks the column name and column type, and checks whether the values are null. The data transmission service does not check the value length or default value. 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. After the precheck succeeds, click Start Task.

   If you do not need to start the task now, click Save. You can manually start the task on the Synchronization Tasks page or by performing batch operations later. For more information about batch operations, see Perform batch operations on data synchronization tasks.

   The data transmission service allows you to modify the synchronization objects when a synchronization task is running. For more information, see View and modify synchronization objects and their filter conditions. After the data synchronization task is started, it will be executed based on the selected synchronization types. For more information, see View details of a data synchronization task.

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.

References

• Create an OceanBase data source

• Create a DataHub data source

• Perform batch operations on data synchronization tasks

• View details of a data synchronization task