From Oracle to PostgreSQL

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

  • On-premises databases

  • ECS databases

  • RDS for PostgreSQL

Suggestions

Caution

  • 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.

    • The data being synchronized may be locked by other transactions for a long period of time, resulting in read timeout.

    • When DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.

    • If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.

  • 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:

Table 2 Precautions

Type

Restrictions

Database permissions

  • Source database:

    • Full synchronization requires the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, and SELECT for single tables (GRANT SELECT <userName.tbName> to drsUser)

    • Full+Incremental synchronization:

      To synchronize a container database (CDB) of Oracle 12c or later, you must have the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, SELECT for a single table (GRANT SELECT <userName.tbName> to drsUser), EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, LOGMINING, SELECT ON SYS.COL$, SELECT ON SYS.OBJ$, and SET CONTAINER (GRANT SET CONTAINER TO <userName> CONTAINER=ALL).

      To synchronize a pluggable database (PDB) of Oracle 12c or later, you must have the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, SELECT for a single table (GRANT SELECT <userName.tbName> to drsUser), EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, LOGMINING, SELECT ON SYS.COL$, and SELECT ON SYS.OBJ$, and CREATE SESSION, SELECT ANY DICTIONARY, EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, LOGMINING and SET CONTAINER (GRANT SET CONTAINER TO <userName> CONTAINER=ALL) permissions for a CDB.

      For Oracle 11g and earlier versions, the following permissions are required for database synchronization: CREATE SESSION, SELECT ANY DICTIONARY, SELECT for a single table (GRANT SELECT <userName.tbName> to drsUser), EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, SELECT ON SYS.COL$, and SELECT ON SYS.OBJ$.

    • During incremental synchronization, enable PK, UI, or ALL supplemental logging for the source Oracle database at the database level or table level. If supplemental logging is enabled at table level, enable supplemental logging again after you rebuild or rename tables. During the synchronization, ensure that the preceding settings are always enabled.

  • The destination database user must have the following permissions: INSERT, SELECT, UPDATE, DELETE, CONNECT, CREATE, and REFERENCES.

Synchronization object

  • Only tables, indexes, and (primary key, null, not null) constraints can be synchronized. Views, foreign keys, stored procedures, triggers, functions, events, and virtual columns cannot be synchronized.

  • In the full synchronization phase, bfile, xml, sdo_geometry, urowid, interval (precision greater than 6 digits), and user-defined types are not supported.

  • In the incremental synchronization phase, bfile, xml, interval, sdo_geometry, urowid, timestamp (precision greater than 6 digits), and user-defined types are not supported.

  • For the TIMESTAMP WITH TIME ZONE data type, the data cannot be greater than 9999-12-31 23:59:59.999999 after being converted based on the time zone of the destination database.

  • The default values of the source database can be to_date and sys_guid functions. To use other functions as default values, ensure that the destination database has the same functions. If the destination database does not have the corresponding function, the following results may be displayed:

    • The default value may be left empty.

    • The table fails to be created. As a result, the object comparison result is inconsistent or the task fails.

  • If the table contains only LOB columns, data inconsistency may occur.

  • Tables whose default values contain expressions of functions cannot be synchronized.

  • Temporary tables in the source database cannot be synchronized.

Source database

  • The names of databases and tables cannot contain non-ASCII characters or special characters .><\`|,?'!"

  • An empty source database cannot be synchronized.

  • Only the following character sets are supported: ZHS16GBK, AL32UTF8, UTF8, US7ASCII, WE8MSWIN1252, and WE8ISO8859P1.

Destination database

  • The destination DB instance is running properly.

  • The destination DB instance must have sufficient storage space.

  • Do not use foreign keys for tables during incremental synchronization. Otherwise, the sequence of writing data to different tables may be inconsistent with that in the source database, which may trigger foreign key constraints and cause synchronization failures.

Precautions

  • Objects that have dependencies must be synchronized at the same time to avoid synchronization failure.

  • Object names, such as table names, are converted to lowercase letters after being synchronized to the destination database. For example, ABC is converted to abc. In incremental synchronization, the source database cannot contain tables with the same name but different letter cases. Otherwise, the synchronization will fail.

  • If there are special characters in the Oracle database, the code of the destination Oracle database must be the same as the code of the source Oracle database. Otherwise, garbled characters are displayed in the destination database.

  • If a task fails because the (self-built) table structure of a table without primary keys is not synchronized and the task cannot be resumed after the table structure is restored, reset the task.

  • During table structure synchronization, if the destination database has a constraint with the same name as the source database, the table fails to be created.

  • If you use DRS to synchronize table structures, the tables, constraints, and indexes in the same schema cannot have the same name with different letter cases. For example, table A contains an index named inx1, and table B contains an index name a. Table A and index a have the same name with different letter cases, which will cause table structure synchronization to fail. If multiple schemas are mapped to one schema, the source schemas cannot contain tables, constraints, and indexes with the same name but different letter cases.

  • If the Oracle character set is WE8MSWIN1252, the CLOB column synchronized to the destination database may contain garbled characters. You can change the character set of the source database to AL32UTF8 before the synchronization.

  • If the length of a table structure in the Oracle database exceeds 65,535 bytes, the synchronization may fail. The length of a table structure is the total length of all columns. The length of the char or varchar2 type is related to the code.

  • The size of an Oracle archive log file must be greater than the maximum size of a single data record to prevent incremental data parsing exceptions caused by cross-file (more than two log files) of a single data record.

  • For an Oracle RAC cluster, use the scan IP address and service name to create a task. The SCAN IP address can provide better fault tolerance, load capability, and synchronization experience.

  • If the source is an Oracle RAC database and the SCAN IP address is used to configure a DRS task, ensure that the SCAN IP address and DRS node IP address can communicate with all virtual IP addresses of the source database. Otherwise, the connectivity check fails. If the SCAN IP address is not used, the virtual IP address of a node can be used. In this case, DRS logs are parsed only on the RAC node specified by the virtual IP address.

  • If the source is an RAC database, all RAC nodes must be online when incremental synchronization is started for the first time. Otherwise, an error occurs during incremental synchronization.

  • If the source is an RAC database, the number of nodes cannot be increased or decreased during incremental synchronization to avoid incremental synchronization exceptions and ensure strong data consistency.

  • During synchronization, do not delete the username, password, and permissions of the source and destination databases or change the port of the destination database.

  • During the synchronization, do not perform the resetlogs operation on the source Oracle database. Otherwise, data cannot be synchronized and tasks cannot be restored.

  • During synchronization, the rollback operation of the LOB type is not supported. Otherwise, the synchronization task fails.

  • In a full synchronization for the table structure, the length of the char and varchar2 characters in the source database is automatically increased by at least 1.5 times 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 the source and destination databases. For example, if the character set is UTF8, increase the length (byte) by three times by default. If the character set is GBK, increase the length (byte) by two times by default.

  • During full synchronization of the partitioned table structure, the table is converted to a non-partitioned table. During incremental synchronization, operations related to the partitioned table in the source database may fail to be executed in the destination database.

  • Only normal indexes are synchronized when indexes are synchronized. Primary key constraints are synchronized with the table structure.

  • During an incremental synchronization, 0x00 at the end of BLOB and the spaces at the end of CLOB are truncated.

  • During incremental synchronization, some DDL operations are supported.

    • Table-level synchronization supports alter table add column, alter table drop column, alter table rename column, alter table modify column, and truncate table. The modification of default values is not supported.

  • The names of mapped table-level objects are case-insensitive. For example, the ABC table mapped to the destination database will be changed to table abc.

  • When editing the task to add a new table, ensure that transactions of the new table have been committed. Otherwise, transactions that are not committed may fail to be synchronized to the destination database. You are advised to add tables during off-peak hours.

  • During a full synchronization, 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.

    Caution

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

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.

Procedure

This section uses real-time synchronization from Oracle to RDS for PostgreSQL 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, specify the task name, description, and the synchronization instance details, and click Create Now.

    Table 3 Task and recipient description

    Parameter

    Description

    Region

    The region where the synchronization instance is deployed. You can change the region.

    Project

    The project corresponds to the current region and can be changed.

    Task Name

    The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).

    Description

    The description consists of a maximum of 256 characters and cannot contain special characters !=<>'&"\

    Table 4 Synchronization instance settings

    Parameter

    Description

    Data Flow

    Select To the cloud.

    Source DB Engine

    Select Oracle.

    Destination DB Engine

    Select PostgreSQL.

    Network Type

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

    Destination DB Instance

    The RDS for PostgreSQL instance you created.

    Synchronization Instance Subnet

    Select the subnet where the synchronization instance is located. You can also click View Subnet to go to the network console to view the subnet where the instance resides.

    By default, the DRS instance and the destination DB instance are in the same subnet. You need to select the subnet where the DRS instance resides and ensure that there are available IP addresses. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.

    Synchronization Mode

    • Full+Incremental

      This synchronization mode allows you to synchronize data in real time. After a full synchronization initializes the destination database, an incremental synchronization parses logs to ensure data consistency between the source and destination databases.

      Note

      If you select Full+Incremental, data generated during the full synchronization will be continuously synchronized to the destination database, and the source remains accessible.

    • Full

      All database objects and data you selected are synchronized to the destination database at a time. This mode is applicable to scenarios where service interruption is acceptable.

    Tags

    • This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags.

    • After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

    Note

    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

    IP Address or Domain Name

    The IP address or domain name of the source database.

    Note

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

    Port

    The port of the source 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.

    PDB Name

    Container database (CDB) and pluggable database (PDB) are new features in Oracle 12c and later versions. This function is optional, but it must be enabled if you want to migrate only PDB tables.

    Enter the service name, SID, username, and password of the CDB that contains the PDB tables to be migrated.

    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.

    Note

    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.

    Table 6 Destination database settings

    Parameter

    Description

    DB Instance Name

    The RDS for PostgreSQL instance you selected when creating the task. The 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 DRS, and will be cleared after the task is deleted. You can change the password if necessary.

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

    Table 7 Synchronization mode and object

    Parameter

    Description

    Flow Control

    Flow Control

    You can choose whether to control the flow.

    • Yes

      You can customize the maximum migration 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 Constraint

    • Data is mandatory.

    • 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

    Select Tables or Databases 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.

    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 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.

      Note

      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 Confirm Task 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

    Started Time

    Set Start Time to Start upon task creation or Start at a specified time based on site requirements.

    Note

    After a synchronization task is started, the performance of the source and destination databases may be affected. You are advised to start a synchronization task during off-peak hours.

  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 image1 in the upper-right corner to view the latest task status.

last updated: 2024-11-21 15:36 UTC - commit: 105d476520f2a8b6ca9dd1aa9879d758c0a628fd