Help Center/ Data Replication Service/ Real-Time Synchronization/ Out of the Cloud/ From GaussDB(for MySQL) to GaussDB(DWS)
Updated on 2024-09-25 GMT+08:00
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From GaussDB(for MySQL) to GaussDB(DWS)

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

Primary/standby GaussDB(for MySQL) instances

GaussDB(DWS) cluster

Precautions

Before creating a synchronization task, read the following notes:

  • 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.
Table 2 Precautions

Type

Restrictions

Database permissions
  • The source database user must have the following permissions: SELECT, SHOW VIEW, EVENT, LOCK TABLES, REPLICATION SLAVE, and REPLICATION CLIENT.
  • The destination database user must have the following permissions: INSERT, SELECT, UPDATE, DELETE, CONNECT, and CREATE.

Synchronization object
  • Only tables, common indexes (B-Tree indexes), and (primary key, null, not null) constraints can be synchronized. Views, foreign keys, stored procedures, triggers, functions, events, virtual columns, unique constraints, and unique indexes cannot be synchronized.
  • Comment is supported in full synchronization mode, but not supported in incremental synchronization mode.
  • The following data types are not supported: XML, geometry, point, lineString, polygon, geometrycollection, multipoint, multilinestring, and multipolygon.
  • Only MyISAM and InnoDB tables can be synchronized.
  • A user-defined table that has no primary key and is a partitioned table cannot be synchronized. Otherwise, the task may fail.
  • Replication tables without primary keys of GaussDB(DWS) cannot be synchronized. If a table to be synchronized is a replication table without a primary key in GaussDB(DWS), the task will fail.
  • The column name of the synchronization object cannot be a field forbidden by GaussDB(DWS), such as CTID, XMIN, CMIN, XMAX, CMAX, TABLEOID, XC_NODE_ID and TID. Otherwise, the task fails.
  • The DDL operation of renaming an unselected table is filtered out during the synchronization. As a result, the task may fail or data may be inconsistent.
    • If you rename table A to the name of table B and tables A and B are selected for synchronization, this RENAME statement will not be filtered out.
    • If you rename table A to the name of table B but table B is not synchronized, this RENAME statement will be filtered out.
    • You are not advised to perform the rename operation in the many-to-one synchronization scenario. Otherwise, the task may fail or data may be inconsistent.
  • Full and incremental synchronizations do not support invisible columns. Invisible columns can be synchronized since MySQL 8.0.23. For example: 
    CREATE TABLE `test11` (
  `id` int NOT NULL,
  `c1` int DEFAULT NULL /*!80023 INVISIBLE */,
  PRIMARY KEY (`id`));

Source database
  • The source database must be the primary node of the primary/standby GaussDB(for MySQL) instance.
  • During the incremental synchronization, the binlog of the source database must be enabled and use the row-based format.
  • If the storage space is sufficient, store the source database binlog for as long as possible. The recommended retention period is three days.
  • If the expire_logs_days value of the source database is set to 0, the synchronization may fail.
  • Enable GTID for the source database. If GTID is not enabled for the source database, primary/standby switchover is not supported. DRS tasks will be interrupted and cannot be restored during a switchover.
  • The source database server-id must be set to a value ranging from 2 to 4294967296.
  • The source database name and table name cannot contain non-ASCII characters, or special characters '<`>/\

Destination database
  • The destination database is running properly.
  • The destination database must have sufficient disk space.
  • The time zone of the destination database must be the same as that of the source database.

Precautions
  • If the DCC does not support instances with 4 vCPUs and 8 GB memory or higher instance specifications, the synchronization task cannot be created.
  • Objects that have dependencies must be synchronized at the same time to avoid synchronization failure. Common association: Indexes reference tables.
  • 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.
  • In MySQL, different tables in the same database (schema) can have the same index name or constraint name. In GaussDB(DWS), 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 original index name in the table is changed to the following format after synchronization: hash value + original index name (which may be truncated) + _key. The hash value is calculated based on the original database name_original table name_original index name. Similarly, the original constraint name in the table is changed to the following format after synchronization: hash value + original constraint name (which may be truncated) + _key, or table name_original index name.
  • In the full synchronization phase, only B-Tree indexes are synchronized. Other indexes are not synchronized by default. If there are too many GaussDB(DWS) indexes, the storage space and data import performance will be affected. You are advised to create indexes based on service requirements.
  • If there is a unique key when a table without a primary key is synchronized, data may fail to be written due to data conflicts.
  • If the character sets of the source and destination databases are different, data may be inconsistent or synchronization may fail.
  • If the data types are incompatible, the synchronization may fail.
  • Before creating a DRS task, if concurrency control rules of SQL statements are configured for the source database, the DRS task may fail.
  • Cascade operations cannot be performed on tables with foreign keys. If the foreign key index of a table is a common index, the table structure may fail to be created. You are advised to use a unique index.
  • The source database cannot be restored.
  • Binlogs cannot be forcibly deleted. Otherwise, the synchronization task fails.
  • 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.
  • The source database does not support the reset master or reset master to command, which may cause DRS task failures or data inconsistency.
  • During real-time synchronization, you can change the port number. If the synchronization task fails after the port is changed, you can retry the synchronization task.
  • During real-time synchronization, the IP address, account, and password cannot be changed.
  • During incremental synchronization, the following DDL operations are supported by default:
    • In one-to-one synchronization, the following DDL operations are synchronized by default: CREATE_TABLE, RENAME_TABLE, ADD_COLUMN, MODIFY_COLUMN, ALTER_COLUMN, DROP_CONSTRAINT, ADD_CONSTRAINT, CREATE_INDEX, DROP_INDEX, RENAME_INDEX, and RENAME_COLUMN. You can select the DDL operations to be synchronized on the object selection page as required.
    • If you rename a column in many-to-one synchronization, you must stop services. Otherwise, data inconsistency may occur.
    • In many-to-one scenarios, you are advised to synchronize ADD_COLUMN only. Other DDL synchronization may cause task failures or data inconsistency due to destination table changes.
    • In many-to-one scenarios, when running ADD_COLUNM, ensure that the types of columns added to each table are the same. Otherwise, the task may fail.
    • The name of a table, column, or index to be added or modified cannot exceed 63 characters. Otherwise, the task fails.
    • When an index is creating using a DDL statement, if the table name and index name in the statement contain more than 63 characters, duplicate names may occur. As a result, the index fails to be created.
    • If a primary key is added to a table that does not have a primary key in the source database, the DDL operation must contain the first column. Otherwise, the task fails.
    • When a DDL operation is performed in the incremental phase, if the destination table is not found, the DDL operation will be ignored.
    • In the incremental phase, if CHANGE COLUMN is performed in the source database to modify a column and the column is a distribution column in destination GaussDB(DWS), the statement will be ignored because GaussDB(DWS) does not support distribution column modification.
    • In the incremental phase, the RENAME INDEX operation is not supported because the index rules of the source and destination databases are different.
    • In the incremental phase, you are not advised to combine CHAR(0) with other characters for data synchronization. For example, inserting CONCAT('a',CHAR(0),'b') may cause data inconsistencies.
    • In the incremental phase, you are not advised to combine CHAR(34) (double quotation marks) and CHAR(92) (backslash) with other characters for JSON data synchronization. For example, inserting JSON_OBJECT('$.0', CONCAT('a', CHAR(34), 'b')) may cause data inconsistencies because an extra backslash (\) will be added after it is synchronized to the destination end.
  • During an incremental synchronization, database-level synchronization does not support online DDL, and table-level synchronization supports only online DDL generated by Alibaba Cloud DMS.
  • During an incremental synchronization, tables whose primary key type is binary, text, blob, or clob cannot be deleted or updated.
  • Set the expire_log_day parameter to a proper value to ensure that the binlog does not expire before data transfer resumes. This ensures that services can be recovered after interruption.

Procedure

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

    • Task information description
      Figure 1 Synchronization task information
      Table 3 Task information

      Parameter

      Description

      Region

      The region where the replication instance is deployed. You can change the region.

      Project

      The project corresponds to the current region and can be changed.

      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 details
      Figure 2 Synchronization instance details
      Table 4 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Select Out of the cloud.

      Source DB Engine

      Select GaussDB(for MySQL).

      Destination DB Engine

      Select GaussDB(DWS).

      Network Type

      The 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.

      Source DB Instance

      An available GaussDB(for MySQL) 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.

      Synchronization Mode
      • 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.

      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. The number of specified EIPs must be the consistent with that of DB instances.

      For details about the data transfer fee generated using a public network, see EIP Price Calculator.
    • Task type
      Figure 3 Task type
      Table 5 Task type information

      Parameter

      Description

      Specifications

      DRS instance specifications. Different specifications have different performance upper limits. For details, see Real-Time Synchronization.

      NOTE:

      DRS allows you to upgrade specifications only for single-AZ synchronization tasks. Task specifications cannot be downgraded. For details, see Changing Specifications.

      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.
    • Enterprise Project and Tags
      Figure 4 Enterprise projects and tags
      Table 6 Enterprise Project and Tags

      Parameter

      Description

      Enterprise Project

      An enterprise project you would like to use to centrally manage your cloud resources and members. Select an enterprise project from the drop-down list. The default project is default.

      For more information about enterprise project, see Enterprise Management User Guide.

      To customize an enterprise project, click Enterprise in the upper right corner of the console. The Enterprise Project Management Service page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.

      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.

    Figure 5 Source database information
    Table 7 Source database settings

    Parameter

    Description

    DB Instance Name

    The GaussDB(for MySQL) instance you selected when creating the task. This parameter 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 the system and will be permanently deleted after the task is deleted.

    Figure 6 Destination database information
    Table 8 Destination database settings

    Parameter

    Description

    IP Address or Domain Name

    The IP address or domain name of the destination database.

    Port

    The port of the destination database. Range: 1 - 65535

    Database Username

    The username for accessing the destination database.

    Database Password

    The password for the database username.

    The IP address, username, and password of the destination database are encrypted and stored in the system. After the task is deleted, the information is permanently deleted.

  4. On the Set Synchronization Task page, select the synchronization object type and synchronization object. Click Next.

    Only whitelisted users can synchronize incremental DDL operations. You need to submit a service ticket to apply for this function. In the upper right corner of the management console, choose Service Tickets > Create Service Ticket to submit a service ticket.

    Figure 7 Synchronization mode

    Table 9 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 customize the maximum synchronization speed. During the full synchronization, the synchronization speed of each task (or each subtask in multi-task mode) does not exceed the value of this parameter.

      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 three 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.

      Figure 8 Flow control
    • 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.

    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.

    Data Synchronization Topology

    Data synchronization supports multiple synchronization topologies. You can plan your synchronization instances based on service requirements. For details, see Data Synchronization Topologies.

    Synchronize DDLs

    DDL type for incremental synchronization. You can select Default or Custom based on your service requirements.

    • Default
      • During database-level synchronization, all DDL operations in the binlog related to database objects, except DDL related to permissions, are synchronized to the destination. Common DDL statements are CREATE_TABLE and RENAME_TABLE.
      • During table-level synchronization, only DDL operations in the binlog related to the selected tables are synchronized. Common DDL statements are ADD_COLUMN, MODIFY_COLUMN, and ALTER_COLUMN.
    • Custom: You can select the DDL type to be synchronized as required. The DDL types supported by different data flow types are displayed on the GUI.
    NOTE:
    • Only whitelisted users can synchronize incremental DDL operations. You need to submit a service ticket to apply for this function. In the upper right corner of the management console, choose Service Tickets > Create Service Ticket to submit a service ticket.
    • One-to-one and one-to-many scenarios: If the DDL usage of the source and destination databases must be consistent, high-risk DDLs must be synchronized. If you do not want a high-risk DDL to be performed in the destination, deselect the high-risk DDL to protect destination data. However, this may cause the synchronization to fail. However, filtering DDL may cause synchronization to fail, for example, column deletion.
    • Many-to-one scenarios: Synchronize only the Add Column operation, or tasks may fail or data may be inconsistent due to changes in destination tables.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables, Import object file, or Databases for Synchronization Object as required.

    • If the synchronization objects in source and destination databases have different names, you can map the source object name to the destination one. For details, see Changing Object Names (Mapping Object Names).
      • In the many-to-one scenario, if you want to change the saved database mapping name during table-level synchronization, you need to expand the database.
    • For details about how to import an object file, see Importing Synchronization Objects.
      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 Data Processing page, select the table object to be processed, click Add in the Operation column, enter the column name, type, and operation type, confirm the information, and click Next. You can configure related rules by referring to Processing Data.

    Figure 9 Processing data

    • If you fill in a new column in serverName@database@table format, the new column and the primary key of the source table form a composite primary key.

  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.

      For details about how to handle check failures, see Solutions to Failed Check Items in Data Replication Service User Guide.

    • 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, Send Notifications, SMN Topic, Delay Threshold (s), and Stop Abnormal Tasks After, confirm that the configured information is correct, select the check box before the agreement, and click Submit to submit the task.

    Figure 10 Task startup settings

    Table 10 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.

    Send Notifications

    This parameter is optional. After enabled, select a SMN topic. If the status, latency metric, or data of the migration task is abnormal, DRS will send you a notification.

    SMN Topic

    This parameter is available only after you enable Send Notifications and create a topic on the SMN console and add a subscriber.

    For details, see Simple Message Notification User Guide.

    Delay Threshold (s)

    During an incremental synchronization, a synchronization delay indicates a time difference (in seconds) of synchronization between the source and destination database.

    If the synchronization delay exceeds the threshold you specify, DRS will send alarms to the specified recipients. The value ranges from 0 to 3,600. To avoid repeated alarms caused by the fluctuation of delay, an alarm is sent only after the delay has exceeded the threshold for six minutes.

    NOTE:
    • If the delay threshold is set to 0, no notifications will be sent to the recipient.
    • In the early stages of an incremental synchronization, the synchronization delay is long because a large quantity of data is awaiting synchronization. In this case, no notifications will be sent.
    • Before setting the delay threshold, enable Send Notifications.

    Data Exception Notification

    This parameter is optional. After enabled, DRS will send a notification if the task data is abnormal.

    Stop Abnormal Tasks After

    Number of days after which an abnormal task is automatically stopped. The value must range from 14 to 100. The default value is 14.

    NOTE:
    • You can set this parameter only for pay-per-use tasks.
    • Tasks in the abnormal state are still charged. If tasks remain in the abnormal state for a long time, they cannot be resumed. Abnormal tasks run longer than the period you set (unit: day) will automatically stop to avoid unnecessary fees.

  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: Out of the Cloud