Help Center/ Data Replication Service/ User Guide (Kuala Lumpur Region)/ Real-Time Synchronization/ To the Cloud/ From DDM to GaussDB Centralized
Updated on 2025-08-07 GMT+08:00
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From DDM to GaussDB Centralized

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

DDM instances

GaussDB Centralized (B-compatible or M-compatible) (The database kernel version is 505.2 or earlier.)

Database Account Permission Requirements

To start a synchronization task, the source and destination database users must meet the requirements in the following table. Different types of synchronization tasks require different permissions. For details, see Table 2. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

Table 2 Database account permission

Type

Full and Full+Incremental

Source database user
  • The user of the source DDM database must have at least one permission, for example, SELECT.
  • The DDM sharded database user must have the SELECT, LOCK TABLES, REPLICATION SLAVE, and REPLICATION CLIENT permissions.

Destination database user
  • Database-level permissions: Log in to the postgres base database as user root or other DATABASE users with the Sysadmin role, and grant the CREATE and CONNECT permissions to user DATABASE.

    Statement: GRANT CREATE, CONNECT ON DATABASE <database> TO <user>

  • Schema-level permissions: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the database, and grant the CREATE and USAGE permissions of the schema to the user.

    Statement: GRANT CREATE, USAGE ON SCHEMA <schema> TO <user>

  • Table-level permissions: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the database, and grant the DML permission for tables in the schema to the user. (The SELECT permission is required only for tables without primary keys.)

    Statement for granting the DML permission on all tables in the schema: GRANT SELECT, UPDATE, INSERT, DELETE, INDEX, ALTER ON ALL TABLES IN SCHEMA <schema> TO <user>

    Statement for granting the DML permission on a specified table in the schema: GRANT SELECT, UPDATE, INSERT, DELETE, INDEX, ALTER ON TABLE <schema.table> TO <user>

  • If gs_loader is used to create system catalogs (such as public.pgxc_copy_error_log and public.gs_copy_summary) in the destination database, the all privilege permission is required for accessing the system catalogs.
  • You are advised to create an independent database account for DRS task connection to prevent task failures caused by database account password modification.
  • After changing the account passwords for the source and destination databases, modify the connection information of the DRS task by referring to Modifying Connection Information to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.

Supported Synchronization Objects

Table 3 lists the objects that can be synchronized in different scenarios. DRS will automatically check the objects you selected before the synchronization.

Table 3 Supported synchronization objects

Type

Precautions

Synchronization objects
  • Full synchronization supports the synchronization of data, table structures, and indexes.
  • The source database cannot contain tables whose sharding keys are of the timestamp type.
  • The sharding key of the source table must be added to the primary key and unique key of the destination table, which means that the primary key and unique key columns of the destination table must contain the sharded columns of the source table to avoid data conflict and inconsistency.
  • The names of the source databases, tables, and columns cannot contain non-ASCII characters or the following characters: <'>/\
  • Index names in the source database cannot contain double quotation marks (").
  • The column names in the source database tables cannot end with a backslash (\).
  • Only MyISAM and InnoDB tables can be synchronized.
  • Virtual columns are synchronized as common columns, and no data is written or incremental synchronization is performed.
  • Other database objects such as stored procedures cannot be synchronized.

Precautions

To ensure tasks can run normally, DRS provides automatic pre-check. Before starting a DRS task, DRS checks the configurations and conditions of the source and destination databases. For details about the main check items and handling suggestions, see Pre-check Items. In addition to the pre-check items, you need to pay attention to the items listed in Table 4.

Table 4 Precautions

Type

Restrictions

Restrictions on the source database
  • Enable skip-name-resolve for the source sharded database to reduce the possibility of connection timeout.
  • The source physical sharded database does not support the enumeration and set types.
  • The default value in the timestamp column of the source database must be within the range allowed by the destination database. Otherwise, the synchronization fails.

Restrictions on usage

General

  • During the synchronization, do not change the sharding key of a table on the source DDM instance, or change an unsharded or broadcast table to a sharded table, or change a sharded table to an unsharded or broadcast table.
  • The source database cannot be restored.

Full synchronization

  • When a DRS task is being started or in the full synchronization phase, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.
  • During table structure synchronization of full synchronization, the auto-increment attribute of the table structure is not synchronized for data synchronization from DDM to GaussDB (PostgreSQL-compatible).
  • During table structure synchronization in a full synchronization, the column name cannot be CTID, XMIN, CMIN, XMAX, CMAX, TABLEOID, XC_NODE_ID, TID, OID, GS_TUPLE_UID or TABLEBUCKETID. Otherwise, the table fails to be created.
  • When the structure of a partitioned table is synchronized during a full synchronization, the partitioned table is converted to a non-partitioned table. During incremental synchronization, operations on partitioned tables in the source database cannot be synchronized to the destination database.

Incremental synchronization

  • Do not modify or delete the usernames, passwords, and permissions of the source and destination databases or change the ports of the source and destination databases.
  • DDL operations cannot be synchronized.
  • If you need to modify the structure of the source table to be synchronized, you must modify the corresponding destination table structure.
  • Perform DDL operations on the same table or column during off-peak hours at an interval of more than 1 minute.
  • Tables whose primary key type is binary, text, blob, or clob cannot be deleted or updated on the destination database.

Other restrictions
  • In DDM, different tables in the same database (schema) can have the same index name or constraint name. In GaussDB, the index and constraint names are unique in the same schema, and the length is limited. To prevent conflicts between index and constraint names, the index name synchronized to the destination table is in the following format: table name + original index name. If the name is too long, it will be changed to idx_ + hash value. The hash value is calculated based on the original table name_original index name.
  • If the source database contains a duplicate primary key, data synchronized to the destination database will be less than that in the source database. You must check and correct the data before starting the synchronization task.
  • If a table in the source database contains system columns _ddm_lock and _slot, data in these columns will be filtered out during full synchronization and incremental synchronization, resulting in data loss.
  • If the network is reconnected within 30 seconds, real-time synchronization will not be affected. If the network is interrupted for more than 30 seconds, the synchronization task will fail.
  • After a table in the source database is synchronized to the destination database, the table is distributed in hash mode and cannot be replicated.
  • Before creating a DRS task, if concurrency control rules of SQL statements are configured for the source database, the DRS task may fail.
  • The destination table can contain more columns than the source table. However, the following failures must be avoided:
    • Assume that extra columns on the destination database cannot be null or have default values. If newly inserted data records are synchronized from the source database to the destination database, the extra columns will become null, which does not meet the requirements of the destination database and will cause the task to fail.
    • Assume that extra columns on the destination database must be fixed at a default value and have a unique constraint. If newly inserted data records are synchronized from the source database to the destination database, the extra columns will contain multiple default values. That does not meet the unique constraint of the destination database and will cause the task to fail.
  • The changes to the source database cannot be synchronized to the destination database in multiple tasks at the same time. Otherwise, data inconsistency and synchronization failure may occur.
  • Only the database-level character set can be set for GaussDB. If the table-level and field-level character sets are set for DDM, the table structure may fail to be created due to character length differences.
  • In a full synchronization for the table structure, the length of char, varchar, nvarchar, enum, and set characters in the source database automatically increases by byte in the destination database (because the length of the destination database is in the unit of byte). The increase multiple depends on the character set of columns in the source database. For example, if the character set of the source database is UTF8, increase the length (byte) by three times. If the character set of the source database is UTF8MB4, increase the length (byte) by four times.
  • Do not use an imprecise value type as the primary key in the database. This feature affects the synchronization of UPDATE and DELETE statements in the DRS incremental scenario.
  • If a table without a primary key contains large fields (tinyblob, blob, mediumblob, longblob, tinytext, text, mediumtext, longtext, clob, nclob, bytea and binary), data of the large fields may be inconsistent during incremental synchronization.
  • If a time type is used as a primary key and the value of the time type is an invalid value of the destination database, data inconsistency or task failure may occur during incremental synchronization.
  • Floating-point data is approximate numbers and depends on the OS platform and underlying implementation. FLOAT and DOUBLE data is inaccurate. If you synchronize floating-point data between DDM physical nodes and GaussDB, there may be some differences. For details, see the official MySQL documentation.
  • DDM and GaussDB process zero time (0000-00-00 00:00:00) in different ways. During value comparison, if there is zero time in the source or destination database, the comparison result shows that data is inconsistent.
  • If a table in the source DDM database contains a binary field with a fixed length, the MySQL driver adds \0 to the end of the data based on the length. As a result, there may be data inconsistency after the data is synchronized to the destination GaussDB database.
  • If the source database contains non-standard floating-point data and the data can be written in loose mode but cannot be written in strict mode, there may be data inconsistency during synchronization.
  • If the source table to be synchronized has the AUTO_INCREMENT attribute, DRS automatically updates the start value of the GaussDB auto-increment sequence corresponding to the integer sequence of the table when the task is complete. The updated value is the maximum value of the sequence plus 10,000.
  • As there are syntax differences between heterogeneous databases and between GaussDB databases of different versions, incremental DDL synchronization may cause task failures or data inconsistency. For details, see the GaussDB Compatibility Description of the destination database.
  • Hash and key partitions depend on the hash algorithm of heterogeneous databases. If TRUNCATE PARTITION is executed on a table that contains hash or key partitions, the data will be inconsistent.
  • If the table structure has been created in the destination database and the column value range of the destination database is smaller than that of the source database, data may be truncated or the default compatibility of the number type may be converted, causing task failures or data inconsistency.
  • If the time type is used as a primary key and there is abnormal data (data beyond the range from 00:00:00 to 23:59:59), the value comparison result may be inconsistent.
  • Whether to convert empty strings written to the destination database depends on the compatibility mode of the destination database. For example, empty strings are automatically converted to null during synchronization to GaussDB (A-compatible mode).
  • After a task is created, you cannot add schemas to the source database or modify the old schema to associate with the new RDS DB instance. Otherwise, data cannot be synchronized or the task fails.

Procedure

This section uses real-time synchronization from DDM to GaussDB Centralized as an example to describe how to configure a real-time synchronization task.

  1. On the Data Synchronization Management page, click Create Synchronization Task.
  2. On the Create Synchronization Instance page, specify the task name, description, and the synchronization instance details, and click Create Now.

    • Task information description
      Table 5 Task information

      Parameter

      Description

      Task Name

      The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).

      Description

      The description consists of a maximum of 256 characters and cannot contain special characters !=<>'&"\
    • Synchronization instance information

      Table 6 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Select To the cloud.

      Source DB Engine

      Select DDM.

      Destination DB Engine

      Select GaussDB Centralized.

      Network Type

      Public network is used as an example. Available options: VPC, Public network and VPN or Direct Connect

      • VPC is suitable for data synchronization between cloud databases of the same account in the same region and VPC.
      • Public network is suitable for data synchronization from on-premises or external cloud databases to the destination databases bound with an EIP.
      • VPN or Direct Connect is suitable for data synchronization from on-premises databases to cloud databases, between databases of different accounts in the same region on the cloud, or between databases across regions on the cloud using a VPN, Direct Connect, Cloud Connect, VPCEP, or a VPC peering connection.

      Destination DB Instance

      An available GaussDB Centralized instance.

      Synchronization Instance Subnet

      Select the subnet where the synchronization instance is located. You can also click View Subnets to go to the network console to view the subnet where the instance resides.

      By default, the DRS instance and the destination DB instance are in the same subnet. You need to select the subnet where the DRS instance resides, and there are available IP addresses for the subnet. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.

      IP Address Type

      The IP address type of the synchronization instance. IPv4 and IPv4/IPv6 dual stack are available.

      • IP Address Type can be set to IPv4/IPv6 dual stack only when IPv4/IPv6 dual stack is enabled for the selected VPC and subnet.
      • If you select IPv4/IPv6 dual stack and the source or destination database is connected by selecting an instance, DRS preferentially uses an IPv4 address to access the database.

      Synchronization Mode

      The synchronization mode supported by a DRS task. Full+Incremental is used as an example.

      • Full+Incremental

        This synchronization mode allows you to synchronize data in real time. After a full synchronization initializes the destination database, an incremental synchronization parses logs to ensure data consistency between the source and destination databases.

        NOTE:

        If you select Full+Incremental, data generated during the full synchronization will be continuously synchronized to the destination database, and the source remains accessible.

      • Full

        All objects and data in non-system databases are synchronized to the destination database at a time. This mode is applicable to scenarios where service interruption is acceptable.

      Specify EIP

      This parameter is available when you select Public network for Network Type. Select an EIP to be bound to the DRS instance. DRS will automatically bind the specified EIP to the DRS instance and unbind the EIP after the task is complete.
    • Task type
      Figure 1 Task type
      Table 7 Task type information

      Parameter

      Description

      AZ

      Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.
    • Tags

      Table 8 Tags

      Parameter

      Description

      Tags
      • Tags a task. This configuration is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags.
      • If your organization has configured tag policies for DRS, add tags to tasks based on the policies. If a tag does not comply with the policies, task creation may fail. Contact your organization administrator to learn more about tag policies.
      • After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

    If a task fails to be created, DRS retains the task for three days by default. After three days, the task automatically stops.

  3. On the Configure Source and Destination Databases page, wait until the synchronization instance is created. Then, specify source and destination database information and click Test Connection for both the source and destination databases to check whether they have been connected to the synchronization instance. After the connection tests are successful, select the check box before the agreement and click Next.

    Table 9 Source database settings

    Parameter

    Description

    DB Instance Name

    The DDM instance you selected when you create a synchronization task. The instance name cannot be changed.

    Database Username

    The username for accessing the source database.

    Database Password

    The password for the database username.

    The username and password of the source database are encrypted and stored in DRS and will be cleared after the task is deleted.

    Table 10 Destination database settings

    Parameter

    Description

    DB Instance Name

    The GaussDB Centralized instance selected during synchronization task creation. This parameter cannot be changed.

    Database Username

    The username for accessing the destination database.

    Database Password

    The database username and password are encrypted and stored in the system and will be cleared after the task is deleted.

  4. On the Set Synchronization Task page, select synchronization objects and click Next.

    Table 11 Synchronization mode and object

    Parameter

    Description

    Flow Control

    You can choose whether to control the flow. Flow Control takes effect in the full phase only.

    • Yes

      You can set a maximum synchronization speed, which varies depending on network conditions. During the synchronization, the synchronization speed of each task (or each subtask in multi-task mode) will not exceed the threshold you configure.

      In addition, you can set the time range based on your service requirements. The traffic rate setting usually includes setting of a rate limiting time period and a traffic rate value. Flow can be controlled all day or during specific time ranges. The default value is Always. A maximum of 10 time ranges can be set, and they cannot overlap.

      The flow rate must be set based on the service scenario and cannot exceed 9,999 MB/s.

    • No
      The synchronization speed is not limited and the outbound bandwidth of the source database is maximally used, which will increase the read burden on the source database. For example, if the outbound bandwidth of the source database is 100 MB/s and 80% bandwidth is used, the I/O consumption on the source database is 80 MB/s.
      NOTE:
      • The flow control mode takes effect only in the full synchronization phase.
      • You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.

    Synchronization Object Type

    You can select Table structure, Data, or Index for Synchronization Object Type for full synchronization.

    • Data is selected by default.
    • If Table structure is selected, the destination database cannot contain tables whose names are the same as the source tables to be synchronized.
    • If Table structure is not selected, the destination database must have tables that match the source tables, and the table structure must be the same as the selected source table structures.

    Incremental Conflict Policy

    The conflict policy refers to the conflict handling policy during incremental synchronization. By default, conflicts in the full synchronization phase are ignored. Select any of the following conflict policies:

    • Ignore

    The system will skip the conflicting data and continue the subsequent synchronization process. If you select Ignore, data in the source database may be inconsistent with that in the destination database.

    • Overwrite

    Conflicting data will be overwritten.

    Synchronize DML

    Select the DML operations to be synchronized. By default, all DML operations are selected.

    If you do not select Delete, DELETE statements in the incremental data of the source database will not be synchronized, which may cause a data inconsistency. As a result, there may be a data conflict or the task may fail.

    Case Conversion Policy in the Destination Database

    The case conversion involves schema names, table names, column names, additional columns, column processing, and incremental DDL statements. The case conversion is based on the mapped name. To ensure that the case of a name in the destination database is the same as that of a mapped name of a synchronization object, select Consistent.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can synchronize tables based on your service requirements.

    NOTE:
    • To quickly select the desired database objects, you can use the search function.
    • If there are changes made to the source databases or objects, click in the upper right corner to update the objects to be synchronized.
    • If an object name contains spaces, the spaces before and after the object name are not displayed. If there are two or more consecutive spaces in the middle of the object name, only one space is displayed.
    • The name of the selected synchronization object cannot contain spaces.

  5. On the Process Data page, set the filtering rules for data processing.

    • If data processing is not required, click Next.
    • If data processing is required, select Data filtering, Additional Columns, or Processing Columns. Currently, only column processing is supported. For details about how to configure related rules, see Processing Data.

  6. On the Check Task page, check the synchronization task.

    • If any check fails, review the cause and rectify the fault. After the fault is rectified, click Check Again.
    • If all check items are successful, click Next.

      You can proceed to the next step only when all checks are successful. If there are any items that require confirmation, view and confirm the details first before proceeding to the next step.

  7. On the displayed page, specify Start Time, confirm that the configured information is correct, and click Submit to submit the task.

    Table 12 Task startup settings

    Parameter

    Description

    Start Time

    Set Start Time to Start upon task creation or Start at a specified time based on site requirements.

    NOTE:

    After a synchronization task is started, the performance of the source and destination databases may be affected. You are advised to start a synchronization task during off-peak hours.

  8. After the task is submitted, you can view and manage it on the Data Synchronization Management page.

    • You can view the task status. For more information about task status, see Task Statuses.
    • You can click in the upper right corner to view the latest task status.
    • By default, DRS retains a task in the Configuration state for three days. After three days, DRS automatically deletes background resources, but the task status remains unchanged. When you configure the task again, DRS applies for resources for the task again. In this case, the IP address of the DRS instance changes.
    • For a public network task, DRS needs to delete background resources after you stop the task. The EIP bound to the task cannot be restored to the Unbound state until background resources are deleted.

Parent topic: To the Cloud