Help Center/ Data Replication Service/ Real-Time Synchronization/ To the Cloud/ From DDM to MySQL
Updated on 2023-04-26 GMT+08:00
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From DDM to MySQL

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB
  • DDM instances
  • RDS for MySQL

Prerequisites

  • You have logged in to the DRS console.
  • Your account balance is greater than or equal to $0 USD.
  • For details about the DB types and versions supported by real-time synchronization, see Supported Databases.
  • If a subaccount is used to create a DRS task, ensure that an agency has been added. To create an agency, see Agency Management.

Suggestions

  • When a 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.
  • To keep data consistency before and after the synchronization, ensure that no data is written to the destination database during the synchronization.
  • The success of database synchronization depends on environment and manual operations. To ensure a smooth synchronization, perform a synchronization trial before you start the synchronization to help you detect and resolve problems in advance.
  • Start your synchronization task during off-peak hours. A less active database is easier to synchronize successfully. If the data is fairly static, there is less likely to be any severe performance impacts during the synchronization.
    • If network bandwidth is not limited, the query rate of the source database increases by about 50 MB/s during full synchronization, and two to four CPUs are occupied.
    • To ensure data consistency, tables to be synchronized without a primary key may be locked for 3s.
    • The data being synchronized may be locked by other transactions for a long period of time, resulting in read timeout.
    • When DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
    • If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.
    • For more information about the impact of DRS on databases, see What Is the Impact of DRS on Source and Destination Databases?
  • Data-Level Comparison

    To obtain accurate comparison results, start data comparison at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, data inconsistency may occur, reducing the reliability and validity of the comparison results.

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 or destination databases, modify the connection information in the DRS task as soon as possible 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 DDM account must have at least one permission, for example, SELECT. The physical sharded database account 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: SELECT, CREATE, ALTER, DROP, DELETE, INSERT, and UPDATE. The root account of the RDS for MySQL DB instance has the preceding permissions by default.

Synchronization object
  • Full synchronization supports the synchronization of data, table structures, and indexes.
  • The source database cannot contain tables whose sharding keys are timestamp.
  • 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.

Source database
  • During the incremental synchronization, the binlog of the source sharded 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.
  • During an incremental synchronization, the server_id value of the MySQL source database must be set. If the source database version is MySQL 5.6 or earlier, the server_id value ranges from 2 to 4294967296. If the source database is MySQL 5.7 or later, the server_id value ranges from 1 to 4294967296.
  • The database names and table names of the source database sharding middleware cannot contain the following characters: '<>/\ and non-ASCII characters.
  • Enable skip-name-resolve for the MySQL source database to reduce the possibility of connection timeout.
  • Enable GTID of the source database.

Destination database
  • The destination DB instance is running properly. If the destination DB instance type is primary/standby, the replication status must also be normal.
  • The destination DB instance must have sufficient storage space.
  • If the destination database (excluding MySQL system database) has the same name as the source database, the table structures in the destination database must be consistent with those in the source database.
  • The character set of the destination database must be the same as that of the source database.
  • The time zone of the destination database must be the same as that of the source database.
  • During a synchronization, a large amount of data is written to the destination database. If the value of the max_allowed_packet parameter of the destination database is too small, data cannot be written. You are advised to set the max_allowed_packet parameter to a value greater than 100 MB.

Precautions
  • If the data types are incompatible, the synchronization may fail.
  • Resumable upload is supported, but data may be repeatedly inserted into a table that does not have a primary key when the server system breaks down.
  • If the source database contains a duplicate primary key or unique key, the data synchronized to the destination database will be less than that in the source database. Therefore, you must check and correct the data before starting the synchronization task.
  • If the destination DB instance is an RDS for MySQL instance, tables encrypted using Transparent Data Encryption (TDE) cannot be synchronized.
  • 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 cannot be null or have default values. If newly inserted data records are synchronized from the source to the destination, the extra columns will become null, which does not meet the requirements of the destination and will cause the task to fail.
    • Assume that extra columns on the destination must be fixed at a default value and have a unique constraint. If newly inserted data records are synchronized from the source to the destination, the extra columns will contain multiple default values. That does not meet the unique constraint of the destination and will cause the task to fail.
  • After a task is created, the destination database cannot be set to read-only.
  • 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.
  • During synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases.
  • 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.
  • During incremental synchronization, do not perform the restoration operation on the source database.
  • During incremental synchronization, some DDL operations are supported.
    • DROP_DATABASE, DROP_TABLE, TRUNCATE_TABLE, CREATE_VIEW and DROP_VIEW are not supported.
    • Online DDL is not supported.
    • Tables can be created. For example: 
      create table `ddl_test` (id int, c1 varchar(25), primary key(id));
create table `ddl_test_gho` like `ddl_test`;
    • Tables can be renamed. Both the source and destination tables must be selected. For example: 
      rename table `ddl_test` to `ddl_test_new`;
    • Columns in a table can be added and modified, but cannot be deleted. For example: 
      alter table `ddl_test` add column `c2` varchar(25); 
alter table `ddl_test` modify column `c1` varchar(50);
alter table `ddl_test` alter c1 set default 'xxx';
    • Table indexes can be modified. For example: 
      alter table `ddl_test` drop primary key; 
alter table `ddl_test` add primary key(id); 
alter table `ddl_test` add index  `ddl_test_uk`(id);
alter table `ddl_test` drop index `ddl_test_uk`;
    • In table-level synchronization, you can add columns, modify columns, and add primary keys and normal indexes.
    • During database-level synchronization, you can create tables, rename tables, add columns, modify columns, and add primary keys and normal indexes.
    • The name of a table, column, or index to be added or modified cannot exceed 63 characters. Otherwise, the task fails.
    • 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.
  • During incremental synchronization, perform DDL operations on the same table or column during off-peak hours at an interval of more than 1 minute.

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 and recipient description

      Parameter

      Description

      Region

      The region where the synchronization 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 To the cloud.

      Source DB Engine

      Select DDM.

      Destination DB Engine

      Select MySQL.

      Network Type

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

      Destination DB Instance

      The RDS DB instance you created.

      Synchronization Instance Subnet

      Select the subnet where the synchronization instance is located. You can also click View Subnet 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 ensure that there are available IP addresses. 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.

      Source DB Instance Quantity

      Specifies the number of DB instances bound to the source DDM database. The default value is 2. The value ranges from 1 to 64. Set this parameter based on the site requirements.
    • DRS instance specifications
      Figure 3 Specifications
      Table 5 Specifications

      Parameter

      Description

      Specifications

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

      NOTE:

      Currently, DRS supports specification upgrade only in MySQL-to-MySQL synchronization tasks with single-node DRS instances configured. Task specifications cannot be downgraded. For details, see Changing Specifications.
    • Enterprise Projects and Tags
      Figure 4 Enterprise projects and tags
      Table 6 Enterprise Projects and Tags

      Parameter

      Description

      Enterprise Project

      An enterprise project you would like to use to centrally manage your Global Accelerator resources. 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 Management page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.

      Tags
      • This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 10 tags.
      • 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 ends.

  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

    Middleware IP Address or Domain Name

    The IP address or domain name of the source database.

    Port

    The port of the source database. Range: 1 – 65535

    Middleware Username

    The username of the source DDM instance.

    Middleware Password

    The password for the source DDM instance username.

    SSL Connection

    SSL encrypts the connections between the source and destination databases. If SSL is enabled, upload the SSL CA root certificate.

    NOTE:
    • The maximum size of a single certificate file that can be uploaded is 500 KB.
    • If SSL is not enabled, your data may be at risk.

    DB Instance

    The sharded database details.

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

    Figure 6 Destination database information
    Table 8 Destination database settings

    Parameter

    Description

    DB Instance Name

    The RDS DB instance you selected when creating the synchronization task. 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.

    SSL Connection

    If SSL connection is required, enable SSL on the destination database, ensure that related parameters have been correctly configured, and upload an SSL certificate.

    NOTE:
    • The maximum size of a single certificate file that can be uploaded is 500 KB.
    • If SSL is not enabled, your data may be at risk.

  4. On the Set Synchronization Task page, select the objects to be synchronized, and then click Next.

    Figure 7 Synchronization mode
    Table 9 Synchronization mode and object

    Parameter

    Description

    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.

    • Overwrite

      Conflicting data will be overwritten.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. DRS supports table-level synchronization. You can select data for synchronization 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 the object name contains spaces, the spaces before and after the object name are not displayed. If there are multiple spaces between the object name and the object name, only one space is displayed.
    • The name of the selected synchronization object cannot contain spaces.

  5. 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 Checking Whether the Source Database Is Connected in Data Replication Service User Guide.

    • If all check items are successful, click Next.
      Figure 8 Pre-check

      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.

  6. On the displayed page, specify Start Time, Send Notification, SMN Topic, Synchronization Delay Threshold, 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 9 Task startup settings
    Table 10 Task startup settings

    Parameter

    Description

    Started 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

    SMN topic. This parameter is optional. If an exception occurs during synchronization, the system will send a notification to the specified recipients.

    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.

    Synchronization Delay Threshold

    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 Notification.

    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:

    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.

  7. 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, and the task status remains unchanged. When you restart the task configuration, DRS applies for resources again.

Parent topic: To the Cloud