Help Center/ Data Replication Service/ Real-Time Synchronization/ To the Cloud/ From MySQL to GaussDB Primary/Standby
Updated on 2024-12-01 GMT+08:00
View PDF
Share

From MySQL to GaussDB Primary/Standby

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB
  • On-premises MySQL databases (MySQL 5.5, 5.6, 5.7, and 8.0)
  • ECS-hosted MySQL databases (MySQL 5.5, 5.6, 5.7, and 8.0)
  • Other cloud MySQL databases (MySQL 5.5, 5.6, 5.7, and 8.0)
  • RDS for MySQL (5.5, 5.6, 5.7, 8.0)

GaussDB Primary/Standby (B-compatible or M-compatible) (Version 1.0.0 or later)

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 Synchronization

Full+Incremental Synchronization and Incremental Synchronization

Source database user

SELECT

Statement: GRANT SELECT ON <database>.<table> to <user>;

SELECT, LOCK TABLES, REPLICATION SLAVE, and REPLICATION CLIENT

Statement: GRANT SELECT, LOCK TABLES ON <database>.<table> to drsUser; GRANT REPLICATION SLAVE, REPLICATION CLIENT ON *.* to <user>;

For a full+incremental task, if the source database version is 8.0.2 or later, the XA_RECOVER_ADMIN permission is required to prevent data loss caused by uncommitted XA transactions during startup or task editing.

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.For details, see gs_loader.
  • If the destination database is in M-compatible mode, the Sysadmin role must be configured.

    Authorization statement: ALTER USER <user> SYSADMIN;
  • 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
  • The names of the source databases, tables, and columns cannot contain non-ASCII characters or the following characters: <'>/\
  • The column names in the source database tables cannot end with a backslash (\).
  • Only table structures, table data, and indexes can be synchronized.
  • 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.
  • MySQL tables containing virtual columns cannot be synchronized.
  • 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`));

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
  • The names of the source databases and tables cannot contain non-ASCII characters, or the following special characters: .<'>/\"
  • The source database does not support the reset master or reset master to command, which may cause DRS task failures or data inconsistency.
  • 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.

Restrictions on usage

General

  • The source database cannot be restored.
  • During data synchronization, do not upgrade the source MySQL database across major versions. Otherwise, data may become inconsistent or the synchronization task may fail (data, table structures, and keywords may cause compatibility changes after the cross-version upgrade). You are advised to create a synchronization task again if the source MySQL database is upgraded across major versions.

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 MySQL 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 may fail to be synchronized to the destination database or fail to be executed in the destination database.

Incremental synchronization

  • Do not modify or delete the usernames and permissions of the source and destination databases or change the ports of the source and destination databases.
  • If the session variable character_set_client is set to binary, some data may include garbled characters.
  • During incremental synchronization, the following DDL operations are supported by default: CREATE_TABLE, RENAME_TABLE, ADD_COLUMN, RENAME_COLUMN, MODIFY_COLUMN, CHANGE_COLUMN, ALTER_COLUMN, DROP_INDEX, and RENAME_INDEX. You can select the DDL operations to be synchronized on the object selection page as required.
  • During an incremental synchronization, tables whose primary key type is tinyblob, blob, mediumblob, longblob, tinytext, text, mediumtext, longtext, clob, nclob, bytea, or binary cannot be deleted or updated on the destination database.

Stopping a task

  • Stop a task normally.

    Before a task is completed, ensure that the source and destination databases are connected and pay attention to the synchronization status reported by the synchronization log.

  • Forcibly stop a task.

    If you forcibly stop a task, DRS resources will be released.

Troubleshooting

  • If any problem occurs during task creation, startup, full synchronization, incremental synchronization, or completion, rectify the fault by referring to Troubleshooting.

Other restrictions
  • If the DCC does not support instances with 4 vCPUs and 8 GB of 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.
  • By default, the MySQL-to-GaussDB synchronization task does not support loopback and cascading synchronization. That is, 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.
  • 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 MySQL, 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.
  • For incremental DDL synchronization, the DDL syntax in B compatibility mode is used for data synchronization from MySQL to GaussDB (PostgreSQL-compatible). As a result, incremental synchronization may fail.
  • 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.
  • MySQL 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 MySQL 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.
  • If the table structure is synchronized, column names in the destination database will be converted to lowercase letters by default. If the table to be synchronized already exists in the destination database, the column names of the synchronization object table in the destination database must be in lowercase. If column names in the destination database are required to be case sensitive, choose Service Tickets > Create Service Ticket in the upper right corner of the management console to submit a service ticket.
  • 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.
  • 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.

Procedure

This section uses real-time synchronization from MySQL to GaussDB primary/standby 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 5 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 information
      Figure 2 Synchronization instance information
      Table 6 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Select To the cloud.

      Source DB Engine

      Select MySQL.

      Destination DB Engine

      Select GaussDB Primary/Standby.

      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 primary/standby 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

      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.

      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.

      For details about the data transfer fee generated using a public network, see EIP Price Calculator.
    • Task type
      Figure 3 Task type
      Table 7 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 Project and Tags

      Table 8 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 9 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 10 Destination database settings

    Parameter

    Description

    DB Instance Name

    The GaussDB primary/standby 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 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 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 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.

      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. 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.

    Synchronize

    Incremental DDL synchronization is supported. You can determine whether to synchronize DDLs based on service requirements.

    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.

    Synchronize DDLs

    This parameter is available when Incremental DDLs is selected for Synchronize. Select DDL type for incremental synchronization. You can select Default or Custom based on your service requirements.

    • Default
      • 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.

      If Incremental DDLs is selected for Synchronize, but no DDL type is selected for Custom, DDLs will not be synchronized by default.

    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 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. For details about how to configure related rules, see Processing Data.
    Figure 9 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.

      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 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.

    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: To the Cloud