Updated on 2024-03-28 GMT+08:00

From MySQL to GaussDB Distributed

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

  • On-premises MySQL databases
  • MySQL databases on an ECS
  • MySQL databases on other clouds
  • RDS for MySQL

GaussDB distributed

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.
  • You are advised to start your synchronization task during off-peak hours by setting Start Time to Start at a specified time. 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.
    • The data being synchronized may be locked by other transactions for a long period of time, resulting in read timeout.
    • Due to the inherent characteristics of MySQL, in certain scenarios the performance may be negatively affected. For example, if the CPU resources are insufficient and the storage engine is TokuDB, the read speed on tables may be decreased by 10%.
    • 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, compare data 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 and 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 user must have the following permissions:
    • Full synchronization: SELECT.
    • Full+incremental synchronization and incremental synchronization: SELECT, LOCK TABLES, REPLICATION SLAVE and REPLICATION CLIENT.
  • The destination GaussDB database user must have the following permissions:
    • Database-level permission: 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.
    • Schema-level permission: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the object, and grant the CREATE and USAGE permissions of the schema to the user.
    • Table-level permission: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the object, and grant the SELECT, UPDATE, INSERT, ALTER, INDEX, and DELETE permissions for all tables in the SCHEMA to the 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.For details, see gs_loader.

Synchronization object

  • Only table structures, table data, and indexes can be synchronized. Other database objects such as stored procedures cannot be synchronized.
  • Only tables with primary keys can be synchronized. Tables without primary keys cannot be synchronized.
  • Incremental synchronization does not support synchronization of DDL.
  • MySQL tables containing virtual columns cannot be synchronized.
  • The following data types are not supported: XML, JSON containing the bit type, geometry, point, lineString, polygon, geometrycollection, multipoint, multilinestring, and multipolygon.
  • Tables with storage engine different to MyISAM and InnoDB cannot be synchronized.
  • A user-defined table that has no primary key and is a partitioned table cannot be synchronized. Otherwise, the task may fail.
  • Object names will be converted to lowercase letters after being synchronized to the destination database. Therefore, the selected source database tables cannot contain tables with the same name but different letter cases. Otherwise, the synchronization fails.
  • 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

  • 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 this period is set to 0, the synchronization may fail.
    • If the source database is a self-managed MySQL database, set expire_logs_days to specify the binlog retention period. Set expire_logs_day 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.
    • If the source database is an RDS for MySQL instance, set the binlog retention period by following the instructions provided in RDS User Guide.
  • GTID must be enabled 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.
  • During an incremental synchronization, the server_id value of the MySQL source database must be set. For MySQL 5.7, the value of server_id ranges from 1 to 4294967296.
  • During an incremental synchronization, if the session variable character_set_client is set to binary, some data may include garbled characters.
  • The names of the source databases and tables cannot contain non-ASCII characters, or special characters .<'>/\

Destination database

  • The destination DB instance is running properly.
  • The destination DB instance must have sufficient storage space.
  • The time zone of the destination database must be the same as that of the source database.
  • The mapped database configured for the task must exist in the destination 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.
  • In MySQL, 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 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: hash value + original constraint name (which may be truncated) + _key.
  • Cascading one-way synchronization is not supported. For example, data cannot be synchronized from instance A to instance B and then from instance B to instance C.
  • 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.
  • 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.
  • After a table in the source database is synchronized to the destination database, the table is distributed in hash mode and cannot be replicated.
  • If the source DB instance is an RDS for MySQL instance, tables encrypted using Transparent Data Encryption (TDE) cannot be synchronized.
  • If the source MySQL database does not support TLS 1.2 or is a self-built database of an earlier version (earlier than 5.6.46 or between 5.7.0 and 5.7.28), you need to submit an O&M application for testing the SSL connection.
  • 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 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.
  • 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.
  • 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.
  • 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.
  • During an incremental synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases.
  • During an incremental synchronization, DDLs of the source database cannot be replicated.
  • During an incremental synchronization, do not perform the restoration operation on the source database.
  • During an incremental synchronization, tables whose primary key type is blob, text, clob, nclob, or bytea cannot be deleted or updated.
  • During task startup or full synchronization, you are not advised to perform DDL operations, such as the deletion operation. Otherwise, the 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.
  • The source database does not support the reset master or reset master to command, which may cause DRS task failures or data inconsistency.
  • 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 tables without primary keys contain large fields (BLOB, TEXT, CLOB, NCLOB, or BYTEA), data of the large fields may be inconsistent 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 MySQL and GaussDB, there may be some differences. For details, see the official MySQL documentation.
  • Two-phase commit is not supported.
  • 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.

Procedure

This section uses real-time synchronization from MySQL to GaussDB distributed 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, 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 To the cloud.

      Source DB Engine

      Select MySQL.

      Destination DB Engine

      Select GaussDB Distributed.

      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.
      • 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 synchronization of data between on-premises databases and cloud databases, between cloud databases of different accounts in the same region, or between cloud databases across regions.

      Destination DB Instance

      An available GaussDB distributed instance.

      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 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

      The synchronization mode supported by a DRS task. Full+Incremental is used as an example. For details about the underlying working principles for full or incremental synchronization, see Product Architecture and Function Principles.

      • 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.

      • Incremental

        Through log parsing, incremental data generated on the source database is synchronized to the destination database.

    • 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

    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

    Database Username

    The username for accessing the source database.

    Database Password

    The password for the database 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 disabled, your data may be at risk.

    The 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 GaussDB distributed DB 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.

    Figure 7 Synchronization mode

    Table 9 Synchronization mode and object

    Parameter

    Description

    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.

    • Report error

      The synchronization task will be stopped and fail.

    • Overwrite

      Conflicting data will be overwritten.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables or Import object file 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 Mapping Object Names.
    • 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 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 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. For details about how to configure related rules, see Processing Data.
    Figure 8 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.

      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.
      Figure 9 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.

  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 synchronization task is abnormal, DRS will send 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.