Help Center/ Data Replication Service/ User Guide (Ankara Region)/ Real-Time Synchronization/ Out of the Cloud/ From MySQL to Oracle
Updated on 2024-04-11 GMT+08:00
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From MySQL to Oracle

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB
  • RDS for MySQL
  • On-premises databases
  • ECS databases

Prerequisites

  • You have logged in to the DRS console.
  • For details about the DB types and versions supported by real-time synchronization, see Real-Time Synchronization.

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.
    • 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.
  • 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 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 user must have the following permissions: SELECT, LOCK TABLES, REPLICATION SLAVE, and REPLICATION CLIENT.
  • The destination database user must have the following permissions:

    ALTER ANY INDEX, ALTER ANY TABLE, ALTER SESSION, ANALYZE ANY, COMMENT ANY TABLE, CREATE ANY INDEX, CREATE ANY TABLE, CREATE SESSION, DELETE ANY TABLE, DROP ANY TABLE, INSERT ANY TABLE, SELECT ANY TABLE, SELECT ANY DICTIONARY, SELECT ANY TRANSACTION, UPDATE ANY TABLE, and RESOURCE roles.

Synchronization object
  • Full synchronization supports the synchronization of data, table structures, and indexes.
  • Incremental synchronization supports only data synchronization.
  • Geography data types such as geometry, geometrycollection, linestring, multilinestring, multipoint, point and polygon are not supported.
  • Views, constraints, functions, stored procedures, triggers, and events cannot be synchronized.
  • The system database and event status cannot be synchronized.
  • The destination Oracle database does not support empty strings, so the object to be synchronized cannot contain empty strings.

Source database
  • The source database names cannot contain non-ASCII characters, or the following characters: '<`>/\"
  • The table name in the source database cannot contain non-ASCII characters or the following characters: '<>/\"
  • The source database name or mapped name cannot start with ib_logfile or be ib_buffer_pool, ib_doublewrite, ibdata1 or ibtmp1.
  • During the incremental synchronization, the binlog of the source MySQL 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 an RDS for MySQL instance, set the binlog retention period by following the instructions provided in RDS User Guide.

  • 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.
  • During an incremental synchronization, if the session variable character_set_client is set to binary, some data may include garbled characters.
  • Enable skip-name-resolve for the MySQL source database to reduce the possibility of connection timeout.
  • 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.
  • The source database does not support the mysql binlog dump command.
  • The character set of the source database must be the same as that of the destination database. Otherwise, the synchronization fails.
  • The log_slave_updates parameter of the source database must be enabled. Otherwise, the synchronization will fail.
  • The binlog_row_image parameter of the source database must be set to FULL. Otherwise, the synchronization will fail.
  • If the source MySQL database version is 8.0, do not set lower_case_table_names to 0.
  • The source database cannot be a read replica.

Destination database
  • The destination DB instance is running properly.
  • The destination DB instance must have sufficient storage space.

Precautions
  • The table without a primary key lacks a unique identifier for rows. When the network is unstable, you may need to retry the task several times, or data inconsistency may occur.
  • The NOT NULL constraint of MySQL supports empty strings, while the NOT NULL constraint of Oracle does not. During a synchronization, if an empty string exists in a NOT NULL constraint field, delete the NOT NULL constraint from the destination Oracle database.
  • Before creating a DRS task, if concurrency control rules of SQL statements are configured for the source database, the DRS task may fail.
  • If the default value of the time field in the source database is all 0s, it will be converted to 1970-01-01 00:00:00.
  • If the precision of source database decimal data type exceeds 38, the data will be truncated because the maximum precision of the destination database number data type is 38.
  • The varbinary, binary, and timestamp columns in the source database cannot contain primary key or unique constraints.
  • If the length of the varchar data in the source database is greater than or equal to 667 characters, the varchar type will be converted to the clob type in the Oracle database.
  • All table field names are converted to uppercase letters.
  • 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 destination database cannot be restored to a point in time when a full synchronization was being performed.
  • 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.
  • During task startup or full synchronization, you are not advised to perform DDL operations on the source database.
  • To ensure data consistency, you are not allowed to modify the destination database (including but not limited to DDL operations) during synchronization.
  • During synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases.
  • During the synchronization, the source database cannot write data using the statement-based binlog format.
  • During the synchronization, do not clear binlogs 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.
  • During the synchronization, do not create a database named ib_logfile in the source.
  • During an incremental synchronization, do not perform the point-in-time recovery (PITR) operation on the source database.
  • During incremental synchronization, if the source database is in a distributed transaction, the synchronization may fail.
  • Incremental synchronization filters out all DDL operations.
  • During incremental synchronization, resumable upload is supported, but data may be repeatedly inserted into non-transactional tables that do not have primary keys when the server system breaks down.
  • If table-level synchronization is selected, tables cannot be renamed during incremental synchronization.
  • Set the expire_log_day parameter to a proper value to ensure that the binlog does not expire before data transfer resumes. This ensures that services can be recovered after interruption.

Procedure

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

    • Task information description
      Table 3 Task and recipient description

      Parameter

      Description

      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
      Table 4 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Select Out of the cloud.

      Source DB Engine

      Select MySQL.

      Destination DB Engine

      Select Oracle.

      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.

      Source DB Instance

      The RDS for MySQL 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.

    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.

    Table 5 Source 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 source database.

    Database Password

    The password for the database username.

    SSL Connection

    If SSL connection is required, enable SSL on the source 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 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.

    Table 6 Destination database settings

    Parameter

    Description

    IP Address or Domain Name

    The IP address or domain name of the destination database.

    NOTE:

    For a RAC cluster, use a scan IP address to improve access performance.

    Port

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

    Database Service Name

    Enter a database service name (Service Name/SID). The client can connect to the Oracle database through the database service name. For details about how to query the database service name, see the prompt on the GUI.

    Database Username

    The username for accessing the destination 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 destination database are encrypted and stored in DRS, and will be cleared after the task is deleted.

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

    Table 7 Synchronization mode and object

    Parameter

    Description

    Flow Control

    You can choose whether to control the flow.

    • 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.

    • 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

    Available options: Table structure, Data, and Index

    • 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.

    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.

    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 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.
    • 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.

  6. On the displayed page, specify Start Time, confirm that the configured information is correct, and click Submit to submit the task.

    Table 8 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.

  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 any 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: Out of the Cloud