Data Replication Between Oracle Instances

NineData data replication supports data synchronization between Oracle to Oracle data sources.

Prerequisites

• Ensure that both the source and target data sources have been added to NineData. For instructions on adding data sources, please refer to Add Data Source.

• Check the version numbers of the source and target data sources. Note that the version number of the source data source must be less than or equal to the target data source.

  Source Datasource	Target Datasource
  Oracle 23c	Oracle 23c
  Oracle 21c	Oracle 23c、21c
  Oracle 19c	Oracle 23c、21c、19c
  Oracle 18c	Oracle 23c、21c、19c、18c
  Oracle 12c	Oracle 23c、21c、19c、18c、12c
  Oracle 11g	Oracle 23c、21c、19c、18c、12c、11g

• Supported Oracle versions (product lines) include:

  • Oracle Enterprise Edition
  • Oracle Standard Edition
  • Oracle Express Edition
  • Oracle Personal Edition

• You must have read permissions for the source data source and read-write permissions for the target data source.

• For incremental replication, ensure the following configurations are made in the source data source:

  • Oracle's log mode is set to ARCHIVELOG mode (default is NOARCHIVELOG).

    Verify the current log mode: SELECT log_mode FROM v$database;
    If the log mode is NOARCHIVELOG, perform the following steps:
    1. Shut down the database: SHUTDOWN IMMEDIATE;
    2. Start and mount the database: STARTUP MOUNT;
    3. Execute the command to enable archiving: ALTER DATABASE ARCHIVELOG;
    4. Open the database: ALTER DATABASE OPEN;

  • Supplemental Log is enabled (not enabled by default).

    Verify if supplemental log is enabled: SELECT supplemental_log_data_all allc FROM v$database;
    If it returns NO, execute the command to enable supplemental log:
    - ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
    // Enables supplemental logging at the database level for all tables and columns, consuming more resources.
    - ALTER TABLE <database_name>.<table_name> ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
    // Enables supplemental logging on a specific table, affecting all columns in that table.

Usage Restrictions

• Evaluate the performance of both source and target data sources before executing data synchronization. It is recommended to perform data synchronization during low business hours. Otherwise, full data initialization will consume certain read-write resources from both source and target data sources, leading to an increase in database load.
• Ensure that each table in the synchronized objects has a primary key or unique constraint, and column names are unique. Otherwise, duplicate synchronization of the same data may occur.

Operating Steps

1. Log in to the NineData Console.

2. Click on in the left navigation bar.

3. On the page, click on the in the top right corner.

4. On the tab, configure according to the table below, and click on .

   Parameter	Description
   	Enter the name of the data synchronization task. For easy retrieval and management, use a meaningful name, up to 64 characters.
   	The data source where the sync object is located.
   	The data source that receives the sync object.
   	Choose the content to be copied to the target data source. : Only syncs the table structure of the source data source, without syncing data. : Syncs all objects and data from the source data source, i.e., full data replication. The switch on the right is for toggling periodic full replication. For more information, please refer to Periodic Full Replication. : After full sync, perform incremental sync based on the log of the source data source. The icon represents incremental operation type configuration (not supported by some replication links). You can deselect certain operation types as needed. Once deselected, these operations will be ignored during incremental synchronization.
   	(selected when is selected) : Stop the task when a table with the same name is detected during precheck. : Send a prompt when a table with the same name is detected during precheck and continue the task. During structure replication, ignore this table with the same name. If you are also performing data replication, data will be appended to this table with the same name without overwriting existing data. : Send a prompt when a table with the same name is detected during precheck and continue the task. During structure replication, delete the table with the same name in the target database and replicate the table structure based on the source database. If you are also performing data replication, data will be written after the table structure replication is completed. (optional when performing both structure and data replication): Send a prompt when a table with the same name is detected during precheck and continue the task. During structure replication, keep the table structure in the target database and, when data replication starts, clear the data in the table with the same name and then replicate from the original table. (required when is not selected) : Stop the task when data exists in the target table during precheck. : Ignore this part of the data when data is detected in the target table during precheck and append other data. : Delete this part of the data when data is detected in the target table during precheck and rewrite it.

5. On the tab, configure the following parameters, and then click on .

   Parameter	Description
   	Choose what to copy. You can choose to copy all contents of the source database, or choose to select the contents to be copied in the list and click > to add them to the right list.

6. On the tab, select different actions based on the selected replication type. If updates occur in the source and target data sources during the configuration mapping phase, you can click the button in the upper right corner of the page to refresh the information of the source and target data sources.

   • Includes : Configure the table name after the target table is synchronized to the target data source, and click .

     tip

     You can click on on the right side of the page to customize the name of the columns after synchronization to the target data source. In addition, you can set to configure filter conditions through comparison expressions. Only data that meets the filter conditions will be synchronized to the target data source. For example, setting the filter condition to emp_no>=10005 means that data with emp_no less than 10005 will not be synchronized to the target data source.

   • Excludes : The system automatically selects the same name database in the target data source by default. If it does not exist, you need to manually select the target database. The table names and column names in the target database need to be consistent with the sync objects. If they are not consistent, you can manually map the table names and column names.

7. On the tab, wait for the system to complete the precheck. After the precheck passes, click on .

   tip

   • You can check . After the sync task is completed, automatically initiate data consistency comparison based on the source data source to ensure data consistency on both ends. Depending on your choice of , the timing of starting is as follows:
     • : Initiated after structure replication is completed.
     • + , : Initiated after full replication is completed.
     • + + , : Initiated when the incremental data is first consistent with the source data source and is 0 seconds. You can click on to view the synchronization delay on the page.
   • If the precheck fails, click on on the right side of the target check item to investigate the cause of the failure, manually fix it, and then click to re-execute the precheck until it passes.
   • Items in with can be repaired or ignored depending on the specific situation.

8. On the page, when prompted with , the sync task begins to run. At this point, you can perform the following operations:

   • Click on to view the execution status of each stage of the sync task.
   • Click on to return to the task list page.

View Sync Results

1. Log in to the NineData Console.

2. Click on > in the left navigation bar.

3. On the page, click on the of the target sync task, and the page details are as follows.

   

   Number	Function	Description
   1	Sync Delay	The data synchronization delay between the source and target data sources. A delay of 0 seconds indicates no delay between the two ends, and you can choose to switch the business to the target data source for smooth migration.
   2	Configure Alerts	After configuring alerts, the system will notify you in the way you choose when the task fails. For more information, please refer to Introduction to Operations Monitoring.
   3	More	Pause: Pause the task. Only tasks with the status Running can be paused. Terminate: End unfinished or listening (i.e., incremental sync) tasks. After terminating the task, it cannot be restarted, so please operate with caution. If the synchronized objects contain triggers, the trigger replication options will pop up, please choose as needed. Delete: Delete the task. Once the task is deleted, it cannot be recovered, so please operate with caution.
   4	Structure Replication (displayed in scenarios involving structure replication)	Display the progress and details of structure replication. Click on Logs on the right side of the page: View the execution logs of structure replication. Click on on the right side of the page: View the latest information. Click on View DDL in the Action column on the right side of the target object in the list: View SQL replay.
   5	Full Replication (displayed in scenarios involving full replication)	Display the progress and details of full replication. Click on Monitoring on the right side of the page: View various monitoring indicators during full replication. During the full replication process, you can also click on Flow Control Settings on the right side of the monitoring indicator page to limit the rate of writing to the target data source per second. Click on Logs on the right side of the page: View the execution logs of full replication. Click on on the right side of the page: View the latest information.
   6	Incremental Replication (displayed in scenarios involving incremental replication)	Display various monitoring indicators of incremental replication. Click on on the right side of the page : View the operations currently being executed by the current replication task, including: : The replication task is performed by multiple threads to execute replication operations, showing the current thread number in progress. : Details of the SQL statement currently being executed by the current thread. : The response time of the current thread. If this value increases, it means that the current thread may be stuck for some reason. : The timestamp when the current thread was started. : The current status of the thread. Click on Flow Control Settings on the right side of the page: Limit the rate of writing to the target data source per second. The unit is rows/second. Click on Logs on the right side of the page: View the execution logs of incremental replication. Click on on the right side of the page: View the latest information.
   7	Modify Object	Display modification records of synchronized objects. Click on Modify Sync Object on the right side of the page to configure the synchronization object . Click on on the right side of the page: View the latest information.
   8	Data Comparison	Display the results of data comparison between the source and target data sources. Includes Structure Comparison and Data Comparison. If you have not enabled data comparison, click on Enable Data Comparison on the page. Click on Recompare on the right side of the page: Reinitiate the comparison of current data on both the source and target ends. Click on the date to view the list of all comparison results, and click on the target list item to switch to the details of this comparison result. Click on Logs on the right side of the page: View the execution logs of consistency comparison. Click on Monitoring (only displayed in data comparison): View the trend chart of RPS (records per second compared) during the comparison. Click Details to view earlier records. Click in the Action column on the right side of the comparison list: View the comparison details of the source and target ends. Click (displayed in case of inconsistency): Generate change SQL. You can directly copy this SQL to the target data source to execute and modify the inconsistent content.
   9	Expand	Display detailed information of the current replication task, including Replication Type, Replication Object, Start Time, etc.

Appendix: Pre-Check Item Checklist

Check Item	Check Content
Target Database Same Name Object Existence Check	Check if the objects to be replicated already exist in the target database
Source Data Source Connection Check	Check the status of the source data source gateway, instance accessibility, and accuracy of username and password
Target Data Source Connection Check	Check the status of the target data source gateway, instance accessibility, and accuracy of username and password
Target Database Permission Check	Check if the account permissions in the target database meet the requirements
Source Database Permission Check	Check if the account permissions in the source database meet the requirements
Target Database Data Existence Check	Check if data exists for the objects to be replicated in the target database
Source Database Log Archiving Mode Check	Check if the log archiving mode of the source database is ARCHIVELOG
Source Database Additional Logging Check	Source database additional logging must be enabled and set to ALL

Related Documentation

Introduction to Data Replication