Updated on 2023-04-26 GMT+08:00

From GaussDB Distributed to Oracle

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB

GaussDB distributed

  • On-premises Oracle 11g and 19c databases
  • Oracle 11g and 19c databases on an ECS

Supported Synchronization Objects

Table 2 lists the objects that can be synchronized in different scenarios. DRS will automatically check the objects you selected before the synchronization.

Table 2 Supported synchronization objects

Type

Synchronization Scope

Synchronization scope

  • Instance-level synchronization is not supported. Only one database can be synchronized at a time. To synchronize multiple databases, create multiple tasks.
  • Supported scenarios: full synchronization, incremental synchronization, and full+incremental synchronization.
  • Supported fields: INTEGER, TINYINT, SMALLINT, BIGINT, NUMBER, NUMERIC, REAL, DOUBLE PRECISION, CHARACTER, CHARACTER VARYING, NVARCHAR2, BIT, BIT VARYING, BLOB, BYTEA, CLOB, RAW, TEXT, BOOLEAN, DATE, SMALLDATETIME, TIME WITH TIME ZONE, TIME WITHOUT TIME ZONE, TIMESTAMP WITH TIME ZONE, TIMESTAMP WITHOUT TIME ZONE and MONEY.
  • Table-level synchronization or object file import is supported.
    • During full synchronization, only data in the selected tables can be synchronized.
    • During incremental synchronization, only DML statements of selected tables can be synchronized.
    • Databases without schemas cannot be synchronized.
    • Schemas without tables cannot be synchronized.
    • Column-store tables, compressed tables, delay tables, and temporary tables cannot be synchronized. Do not synchronize unlogged tables in the incremental phase.
    • The database name, schema name, and table name cannot contain special characters /<.>\\'`|\?! The column name cannot contain double quotation marks ("), single quotation marks ('), or periods (.).
    • If you select tables by importing an object file, ensure that the imported table exists in the source database or is visible to the synchronization user.

Database User Permission Requirements

Before you 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 3. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

  • 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.
  • If a distributed database is the source database, the connectivity of each DN needs to be checked. You are advised to perform data synchronization as a non-root database user to prevent user locking due to incorrect password during DN connection.
Table 3 Database user permission

Type

Full

Incremental

Full+Incremental

Source database user

The user has the sysadmin role or the following minimum permissions:

The CONNECT permission for databases, USAGE permission for schemas, SELECT or UPDATE permission for tables, the UPDATE permission for locking tables without primary keys, and SELECT permission for sequences.

The user has the sysadmin role or the following minimum permissions:

The REPLICATION permission or the permission inherited from the built-in role gs_role_replication, the CONNECT permission for databases, the USAGE permission for schemas, and the SELECT permission for tables.

The user has the sysadmin role or the following minimum permissions:

The REPLICATION permission or the permission inherited from the built-in role gs_role_replication, the CONNECT permission for databases, the USAGE permission for schemas, the SELECT or UPDATE permission for tables, the UPDATE permission for locking tables that do not have primary keys, and the SELECT permission for sequences.

Destination database user

The user must have the DBA role or the following minimum permissions:

CREATE SESSION, SELECT and INSERT permissions for tables, or the RESOURCE role.

The user must have the DBA role or the following minimum permissions:

CREATE SESSION, SELECT, INSERT, UPDATE, and DELETE permissions for tables or the RESOURCE role

The user must have the DBA role or the following minimum permissions:

CREATE SESSION, SELECT, INSERT, UPDATE, and DELETE permissions for tables or the RESOURCE role

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.
    • When DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
    • If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.
    • For more information about the impact of DRS on databases, see What Is the Impact of DRS on Source and Destination Databases?
  • Data-Level Comparison

    To obtain accurate comparison results, start data comparison 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

The full+incremental synchronization consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. A single full or incremental synchronization task contains three phases. To ensure smooth synchronization, read the following notes before creating a synchronization task.

Table 4 Precautions

Type

Restrictions

Starting a task

  • Source database parameter requirements:

    If incremental synchronization or full+incremental synchronization is selected:

    • The wal_level parameter of the source database is set to logical.
    • The enable_slot_log parameter of the source database is set to on.
    • The max_replication_slots value of the source database must be greater than the number of used replication slots.
    • Add a primary key to the table that does not have a primary key, or set REPLICA IDENTITY to FULL for the table that does not have a primary key.
  • Source database object requirements:
    • The names of the source database, schema, and table to be synchronized cannot contain special characters /<.>\\'`|\?!
  • Destination database parameter requirements:
    • The source database supports the UTF8 character set, and the destination database supports the AL32UTF8 or UTF8 character set. If the source database uses the GBK or GB18030 character set and the destination database uses the ZHS16GBK, ZHS16CGB231280, or ZHS32GB18030 character set, some characters may be incompatible due to database differences, some data may contain garbled characters, data synchronization may be inconsistent, or data may fail to be written into the destination database.
  • Destination database object requirements:
    • Before synchronization, ensure that the corresponding table structure has been created in the destination database and is the same as that in the source instance. If column processing is performed, ensure the consistency of the table structure after column processing.
    • Triggers enabled in the destination database cannot be associated with synchronization tables.
    • The destination database has sufficient disk space.
    • 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.

  • Other notes:
    • Cascading one-way synchronization is not supported. For example, data cannot be synchronized from instance A to instance B and then from instance B to instance C.
    • During real-time synchronization, the consistency of distributed transactions is not ensured.
    • Synchronization from GaussDB distributed to Oracle is the backward synchronization process for synchronization from Oracle to GaussDB distributed. You are not advised to use either of the two synchronization modes independently.
    • The selected source database cannot contain tables with the same name but different cases. Otherwise, the synchronization fails. You are advised to synchronize only the schema and table names that are in uppercase on the Oracle database, and the schema and table names that are in lowercase on the GaussDB distributed database.
    • Before a task enters the incremental synchronization phase, ensure that long-running transactions are not started in the source database. Starting the long transaction will block the creation of the logical replication slot and cause the task to fail.
    • If a logical replication slot fails to be created or does not exist due to a long transaction, you can reset the task and then restart it.
    • Do not use foreign keys for tables during 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.

Full synchronization

  • Do not change the port of the source and destination databases, or change or delete the passwords and permissions of the source and destination database users. Otherwise, the task may fail.
  • Do not run any DDL statement in the source database. Otherwise, data may be inconsistent or the task may fail.
  • Do not write data to the destination database. Otherwise, data may be inconsistent.

Incremental synchronization

  • Do not change the port of the source and destination databases, or change or delete the passwords and permissions of the source and destination database users. Otherwise, the task may fail.
  • Do not execute any DDL statement in the source database. Restricted by the logical replication function of GaussDB, DDL statements cannot be synchronized. Otherwise, data may be inconsistent or the task may fail.
  • Do not change the REPLICA IDENTITY value of a table in the source database. Otherwise, incremental data may be inconsistent or the task may fail.
  • Do not write data to the destination database. Otherwise, data may be inconsistent.
  • Replication of interval partition tables is not supported.
  • After a DDL statement is executed in a transaction, the DDL statement and subsequent statements are not synchronized.
  • Logical log decoding is restricted by the decoding capability of the GaussDB kernel. For details about the restrictions, see the precautions in "Logical Decoding" of GaussDB Developer Guide.
  • For tables containing large fields (including blob, clob, nclob, long, and long raw), large fields are not used as where conditions for incremental data. You are advised to ensure that all fields except large fields have the unique constraint.
  • If a table in the destination database contains both the lob and long types or both the lob and long raw types, and the length of the long or long raw type to be inserted or updated is greater than 4000, the insertion or update fails. You are advised to use the clob or blob type.

Data processing

  • During column processing, the primary key, unique key, and distribution column cannot be filtered out.

Synchronization comparison

  • You are advised to compare data in the source database during off-peak hours to prevent inconsistent data from being falsely reported and reduce the impact on the source database and DRS tasks.
  • During incremental synchronization, if data is written to the source database, the comparison results may be inconsistent.
  • Data cannot be compared during full synchronization.
  • Do not limit the synchronization speed during data comparison.

Stopping a task

Stop a task normally.

  • After an incremental or full+incremental synchronization is complete, the streaming replication slot created by the task in the source database is automatically deleted.

Forcibly stop a task.

Prerequisites

  • You have logged in to the DRS console.
  • Your account balance is greater than or equal to $0 USD.
  • For details about the DB types and versions supported by real-time synchronization, see Supported Databases.
  • If a subaccount is used to create a DRS task, ensure that an agency has been added. To create an agency, see Agency Management.

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 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 !=<>'&"\

    • Synchronization instance details
      Figure 2 Synchronization instance details
      Table 6 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Choose Self-built to self-built.

      Source DB Engine

      Select GaussDB Distributed.

      Destination DB Engine

      Select Oracle.

      Network Type

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

      VPC

      Select an available VPC.

      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.

      Security Group

      Select a security group. You can use security group rules to allow or deny access to the instance.

      Synchronization Mode

      Available options: Full+Incremental, Full, and Incremental. Full+Incremental is used as an example.

      • 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

        In this mode, data is synchronized from the source to the destination at a time.

      • Incremental

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

      AZ

      Select the AZ where you want to create the DRS instance. Selecting the one housing the source or destination database can provide better performance.

      Source Shard Quantity

      The value must be the same as the number of DNs in the distributed source database. Run the following SQL statement to check the value of Source Shard Quantity:

      SELECT count(DISTINCT node_name) FROM pgxc_node WHERE node_type = 'D';
    • Enterprise Projects and Tags
      Figure 3 Enterprise projects and tags
      Table 7 Enterprise Projects and Tags

      Parameter

      Description

      Enterprise Project

      An enterprise project you would like to use to centrally manage your Global Accelerator resources. 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 Management page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.

      Tags

      • This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 10 tags.
      • 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 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, click Next.

    Establish the connectivity between the DRS instance and the source and destination databases.

    • Network connectivity: Ensure that the source and destination databases accept connections from the DRS instance. To access databases over a public network, configure the database to accept connections from the EIP of the DRS instance. To access databases over a VPC, VPN, or Direct Connect network, configure the database to accept connections from the private IP address of the DRS instance. For details, see Network Preparations.
    • Account connectivity: Ensure that the source and destination databases allows connections from the DRS instance using the username and password.
    Figure 4 Source database information
    Table 8 Source database settings

    Parameter

    Description

    CN IP Address or Domain Name

    Enter the IP addresses of GaussDB. Ensure that the entered IP addresses or domain names belong to the same instance.

    Database Username

    The username for accessing the source database.

    Database Password

    The password for the database username.

    DN IP Address or Domain Name

    You can log in to the CN and run the following SQL statement to query the DN IP address:

    SELECT node_name as dn_name, string_agg(node_host || ':' || node_port, ',' order by node_type) AS dn_ip FROM pgxc_node WHERE node_type != 'C' GROUP BY node_name;

    The resource types of different database instances are different. Therefore, you are advised to contact O&M personnel.

    The username and password of the source 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.

    Figure 5 Destination database information
    Table 9 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 and specify Service Name 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 not enabled, your data may be at risk.

    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 objects to be synchronized, and then click Next.

    Figure 6 Synchronization mode
    Table 10 Synchronization Object

    Parameter

    Description

    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.

      Figure 7 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.

    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.

    • Overwrite

      Conflicting data will be overwritten.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables or Import object files for Synchronization Object 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.
    • 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 Advanced Settings page, set the parameters for full+incremental synchronization selected in 2 and click Next.

    Figure 8 Parameter settings
    Table 11 Full synchronization settings

    Parameter

    Description

    Default Value

    Concurrent Export Tasks

    Number of export threads. Value range: 1 to 16. A larger value indicates higher load on the source database.

    8

    Concurrent Import Tasks

    Number of import threads. Value range: 1 to 16. A larger value indicates higher load on the destination database.

    8

    Rows per Shard

    Value range: 0 or 520,000 to 1,000,000,000

    • 0

      All tables are not sharded, and each table is synchronized as a whole.

    • Other values

      The table is sharded based on the specified value (or the primary key column). If the number of records in a table is less than the value of this parameter, the table is not sharded.

    520000

    Table 12 Incremental synchronization settings

    Parameter

    Description

    Default Value

    Concurrent Replay Tasks

    Number of concurrent threads for data replay. Value range: 1 to 64. Incremental data is concurrently written to the destination database. A larger value indicates higher load on the destination database.

    64

  6. On the Process Data page, set the filtering rules for data processing.

    • If data processing is not required, click Next.
    • If you need process columns or filter out data, set the corresponding rules by referring to Processing Data.
    Figure 9 Processing data

  7. 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 Checking Whether the Source Database Is Connected in Data Replication Service User Guide.

    • If all check items are successful, click Next.
      Figure 10 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.

  8. On the displayed page, specify Start Time, Send Notification, SMN Topic, Synchronization Delay Threshold, 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 11 Task startup settings
    Table 13 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.

    Send Notifications

    SMN topic. This parameter is optional. If an exception occurs during synchronization, the system will send a notification to the specified recipients.

    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.

    Synchronization Delay Threshold

    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 Notification.

    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:

    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.

  9. 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, and the task status remains unchanged. When you restart the task configuration, DRS applies for resources again.