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Updated on 2024-03-28 GMT+08:00
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From MySQL to PostgreSQL

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, and 8.0)

RDS for PostgreSQL (versions 9.5, 9.6, 10, 11, 12, 13, and 14)

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

Source database user

The user must have the following minimum permissions:

SELECT

The user must have the following minimum permissions:

SELECT, LOCK TABLES, REPLICATION SLAVE, and REPLICATION CLIENT

Destination database user

The account of the RDS for PostgreSQL instance has the permissions by default.
  • 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.

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
  • Only table structures, table data, and indexes can be synchronized.
  • Only MyISAM and InnoDB tables can be synchronized.
  • Other database objects such as stored procedures 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 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.

Use restrictions

General

  • If you change the port of the source RDS for MySQL database and the synchronization task fails, retry the task.
  • If the source database is not an RDS for MySQL database, the port cannot be changed.
  • The IP addresses, usernames, and passwords of the source and destination databases cannot be changed.
  • Do not clear binlogs on the source database.
  • Do not perform data restoration on the source database.

Full synchronization phase

  • 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.
  • DRS writes large amount of data to the destination PostgreSQL database. As a result, the number of PostgreSQL WAL logs increases sharply, and the PostgreSQL disk space may be used up. You can disable the PostgreSQL log backup function before the full synchronization to reduce the number of WAL logs. After the synchronization is complete, enable the function. For details, see Setting an Automated Backup Policy.
    CAUTION:

    Disabling log backup will affect database disaster recovery. Exercise caution when performing this operation.

Incremental synchronization phase

  • If the session variable character_set_client is set to binary, some data may include garbled characters.
  • Some DDL statements are supported.
    • Table fields can be added, deleted, and modified. 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.
    • If the destination table is not found, the DDL will be ignored.
    • DROP_DATABASE, DROP_TABLE, TRUNCATE_TABLE, CREATE_VIEW and DROP_VIEW are not supported.
    • Online DDL is not supported.

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
  • MySQL views support syntax "as select ... from a join b where ..." but PostgreSQL does not, which may lead to the synchronization task to fail.
  • 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 PostgreSQL, 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.
  • Objects that have dependencies must be synchronized at the same time to avoid synchronization failure. Common associations: tables or views referenced by views
  • If the source DB instance is an RDS for MySQL instance, tables encrypted using Transparent Data Encryption (TDE) cannot be synchronized.
  • Before creating a DRS task, if concurrency control rules of SQL statements are configured for the source or destination database, the DRS task may fail.
  • 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.
  • You can map multiple databases to one database for synchronization. Tables with the same name cannot exist in mapped databases. To use this function, submit a service ticket. In the upper right corner of the management console, choose Service Tickets > Create Service Ticket to submit a service ticket.
  • Different types of indexes synchronized to the destination database will become B-Tree indexes.
  • If the storage space is sufficient, store the source database binlog files as long as possible. The recommended retention period is three days. If you set the period 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 RDS for MySQL, set the binlog retention period by following the instructions provided in Setting a Local Retention Period for RDS for MySQL Binlogs.
  • 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.
  • Only data that violates the non-null constraint and data of the char or varchar type that exceeds the field length limit can be recorded.
  • 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.
  • If the source table to be synchronized has the AUTO_INCREMENT attribute, DRS automatically updates the start value of the PostgreSQL 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

  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 details
      Figure 2 Synchronization instance details

      Table 6 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Select To the cloud.

      Source DB Engine

      Select MySQL.

      Destination DB Engine

      Select PostgreSQL.

      Network Type

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

      • 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

      The RDS PostgreSQL DB 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.

      • 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.
    • 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 projects 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 Self-build on ECS - source database information

    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 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 10 Destination database settings

    Parameter

    Description

    DB Instance Name

    The RDS PostgreSQL instance you selected when creating the migration task and cannot be changed.

    Database Username

    The username for accessing the destination database.

    Database Password

    The password for the database username.

    The username and password of the destination database are encrypted and stored in the database and the synchronization instance during the synchronization. After the task is deleted, the username and password are permanently deleted.

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

    Figure 7 Synchronization mode

    Table 11 Synchronization 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.

      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 All day. 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. 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.

    Filter DROP DATABASE

    During real-time synchronization, executing DDL operations on the source database may affect the synchronization performance. To reduce the risk of synchronization failure, DRS allows you to filter out DDL operations. Currently, only the delete operations on databases can be filtered by default.

    • If you select Yes, the database deletion operation performed on the source database is not synchronized during data synchronization.
    • If you select No, related operations are synchronized to the destination database during data synchronization.

    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.

    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.

    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 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.

  6. 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 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.

  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, 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.

Parent topic: To the Cloud