GaussDB to GaussDB

NineData Data Replication supports schema replication, full replication, and incremental replication between GaussDB instances.

Overview

NineData data replication supports schema, full data, and incremental data replication between data sources. For supported data sources, it also supports bidirectional replication for geo-distributed active-active architectures.

• Schema replication: Replicates object structures between homogeneous and heterogeneous data sources.
• Full data replication: Uses data sharding and row-level concurrent batch replication to improve throughput. Breakpoint resume helps preserve data accuracy, including for tables without primary keys.
• Incremental data replication: Replicates DML and DDL changes for supported object types. Row-level concurrency and hotspot merge processing help maintain replication throughput.
• Bidirectional real-time data replication (only between MySQL instances): Replicates changes in both directions between nodes so data can stay current across participating nodes.

Use these capabilities for full or incremental data replication, migration, synchronization, data integration, and low-downtime migration workflows.

Before you begin

• Add the source and target data sources to NineData. For instructions, see Add Data Source.

• Both the source and target data sources are GaussDB.

• The target version should not be lower than the source version. Use the same major version on both sides whenever possible. Final compatibility is determined by the precheck.

• Allow the NineData service addresses and database port in the security group or access-control rules of both the source and target GaussDB instances so that connections can be established in both directions. For details, see Setting Security Group Rules for a GaussDB Instance.

• You must have the following permissions on the source and target data sources:

  Replication Type	GaussDB (Source)	GaussDB (Target)
  Schema Replication	CONNECT, SELECT	DDL privileges, or equivalent privileges to create schemas and tables
  Full Replication	CONNECT, SELECT	Read and write privileges on schemas and tables
  Incremental Replication	A high-privilege account that can pass logical replication prechecks	Read and write privileges on schemas and tables

• For incremental replication, make sure the following conditions are met. The logical replication parameters can be adjusted in the parameter template. For details, see the Huawei Cloud document Logical Replication Overview.

  • Add the NineData service addresses to the allowlist of the logical replication node. The service address is displayed below Access Region on the GaussDB data source page.

    

  • The wal_level parameter on the source must be set to logical.

  • The max_replication_slots parameter on the source must be greater than 1. This parameter controls the maximum number of replication slots. The default value is 10.

  • The max_wal_senders parameter on the source must be greater than 1. This parameter controls the maximum number of concurrent replication connections. The default value is 10.

    tip

    Submit a Huawei Cloud support ticket to modify the parameters above.

Restrictions

• Before you run a replication task, assess the performance of the source and target data sources. Run the task during off-peak hours when possible because full initialization consumes read and write resources.
• Each replicated table must have a primary key or unique constraint, and column names must be unique. Otherwise, duplicate rows may be replicated.

Procedure

1. Sign in to the NineData Console.

2. In the left navigation pane, click Replication > Data Replication.

3. On the Replication page, click Create Replication.

4. On the Source & Target tab, configure the fields in the table, and click Next.

   Parameter	Description
   Name	Enter a name for the data synchronization task. To make the task easier to find and manage later, use a meaningful name. Up to 64 characters are supported.
   Source	The data source that contains the objects to synchronize.
   Datahub Project	Select the target Datahub Project. Data from the source data source will be written to the specified Project.
   Type	Select the replication type. Schema: Synchronize only the database and table schemas of the source data source, without synchronizing data. Full: Synchronize all objects and data from the source data source, namely full data replication. The switch on the right enables periodic full replication. For more information, see Periodic Full Replication. Incremental: After full synchronization is complete, perform incremental synchronization based on the logs of the source data source.
   Incremental Started	Required only when Type is Incremental. From Started: Use the current replication task start time as the baseline for incremental replication. Customized Time: Select the point in time from which incremental replication starts. You can select a time zone based on the region of your business. If the configured time point is earlier than the current replication task start time and DDL operations occurred during that period, the replication task will fail.
   Logical replication address (Required when Incremental is selected)	By default, this is the IP address and port number of the source database (port number plus 1 by default). If the connection fails, confirm the replication connection port of your GaussDB instance. For more information, see GaussDB Incremental Synchronization Connection and Port Description. The Logical replication address of GaussDB uses logical decoding to parse WAL logs into a logical log format that is easier to understand and process. NineData receives logs from this address for real-time incremental data synchronization.
   Spec (Unavailable only when Schema is selected)	The specification of the replication task. A larger specification provides a higher replication rate. Hover over the icon to view the rate and configuration information of each specification. Each specification shows the available quantity and total quantity. When the available quantity is 0, the specification is grayed out and cannot be selected.
   If target table already exists (Required when Schema is selected)	Pre-Check Error and Stop Task: Stop the task when a table with the same name is detected during the precheck stage. Skip and Continue Task: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, ignore the table with the same name. If you also perform data replication, data is appended to the table with the same name and existing data is not overwritten. Delete Objects and Rewrite: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, delete the table with the same name in the target database and replicate the table schema again based on the source database. If you also perform data replication, data is written after schema replication is complete.
   Target Table Exists Data (Required when Full is selected)	Pre-Check Error and Stop Task: Stop the task when data is detected in the target table during the precheck stage. Ignore existing target data and append to it.: When data is detected in the target table during the precheck stage, ignore that data and append other data. Clear target existing data before write: When data is detected in the target table during the precheck stage, delete that data and write it again.
   Incremental data conflict handling strategy for target table (Required when Incremental is selected)	Runtime error: During incremental replication, report an error when target data already exists and wait for manual intervention. Do not update target data: During incremental replication, do not write data when target data already exists, and continue subsequent tasks. Update target data: During incremental replication, overwrite the target data when target data already exists.

5. On the Objects tab, configure the parameters in the table, and click Next.

   Parameter	Description

   To create multiple replication tasks with the same replication objects, import a configuration file. Click Import Config, click Download Template to download the template, edit the file, and then click Upload to upload it and import the objects in bulk. The configuration file uses these fields:

   Parameter	Description
   source_table_name	The source table name of the object to synchronize.
   destination_table_name	The target table name that receives the synchronized object.
   source_schema_name	The source schema name of the object to synchronize.
   destination_schema_name	The target schema name that receives the synchronized object.
   source_database_name	The source database name of the object to synchronize.
   target_database_name	The target database name that receives the synchronized object.
   column_list	The list of columns to synchronize.
   extra_configuration	Additional configuration information. This field supports: column_rules: Defines column mappings and value rules. Field descriptions: column_name: Original column name. destination_column_name: Specifies the target column name. column_value: Specifies the column value, which can be an SQL function or a constant value. filter_condition: Specifies row-level data filtering conditions. Only rows that meet the conditions are replicated.

   tip

   • Example of extra_configuration:

     {
       "extra_config":{
         "column_rules":[
           {
              "column_name": "created_time",
              "destination_column_name": "migrated_time",
              "column_value": "current_timestamp()"
           }
         ],
          "filter_condition": "id != 0"
       }
     }

     In this example, created_time is mapped to migrated_time, the target column value is changed to current_timestamp(), and only rows whose id value is not 0 are synchronized.

   • For a complete example of the configuration file, see the downloaded template.

6. On the "Mapping" tab, configure the mapping that matches the selected replication type, then click Save and Pre-Check. If source or target metadata changes while you configure mappings, click Refresh Metadata to refresh the metadata.

   • Includes Schema: Configure the table name after synchronization to the target data source.

   • Does not include Schema: The system selects the database with the same name in the target data source by default. If no such database exists, select the target database manually. The table names and column names in the target database must match the synchronization objects. If they do not match, map the table names and column names manually.

   You can also perform these actions:

   • Click Mapping & Filtering to customize the column names after synchronization to the target data source.
   • On the Mapping & Filtering page, click Data Filter to configure filtering conditions by using comparison expressions. Only data that meets the filtering conditions is synchronized to the target data source. For example, if the filtering condition is set to emp_no>=10005, data whose emp_no column value is less than 10005 is not synchronized to the target data source.
   • Click the icon to the right of "Target Table" to search for a table name and replace it with the target name.
   • Enter a table name in the Search Table text box to quickly locate the target table.
   • Click Batch Configuration to define common rules in batches, such as table name and column name case conversion, prefix or suffix addition, and replacement. Use this option to apply mapping configuration to many tables and columns at the same time.

• Click the drop-down menu to the right of Object Owner to specify the owner of the object. If you do not select an owner, An account with the same name as schema is used by default.

You can also perform these actions:

• Click Mapping & Filtering to customize target column names after synchronization.
• On the Mapping & Filtering page, enter a comparison expression in the text box below Data Filter as the filtering condition. Only data that meets the filtering condition is synchronized to the target data source. For example, if the filtering condition is emp_no>=10005, data whose emp_no column value is less than 10005 is not synchronized to the target data source.
• Click the icon next to "Target Table" to search for table names and replace them with target names.
• Enter a table name in the Search Table text box to quickly locate the target table.
• Click Batch Configuration to define common rules in batches, such as table or column name case conversion, prefix or suffix addition, and replacement. Use batch rules to apply consistent mapping to a large number of tables and columns.

7. On the Pre-check tab, wait for the system to complete the precheck. After the precheck passes, click Launch.

   • Select Enable data consistency comparison to start a data consistency comparison task based on the source data source after synchronization completes. Based on the selected Type, Enable data consistency comparison starts at these times:

     • Schema: Starts after schema replication is complete.
     • Schema+Full: Starts after full replication is complete.
     • Full: Starts after full replication is complete.
     • Schema+Full+Incremental, Incremental: Starts when incremental data is consistent with the source data source for the first time and Delay is 0 seconds. Click View Details to view synchronization delay on the Details page.

   • If the precheck fails, click Details in the Actions column for the failed check item, review the cause, fix the issue, and then click Check Again to run the precheck again until it passes.

   • Items with Warning in Result can be fixed or ignored as needed.

8. On the Launch page, the Launch Successfully message appears, indicating that the synchronization task has started. You can then perform these actions:

   • Click View Details to view the execution status of each stage of the synchronization task.
   • Click Back to list to return to the Replication task list page.

View replication results

1. Sign in to the NineData Console.

2. In the navigation menu, click Replication > Data Replication.

3. On the Replication page, click the Task ID of the target synchronization task. The task details page shows the following information.

   

   Number	Function	Description
   1	Sync Delay	The synchronization delay between the source and target data sources. 0 seconds means the target has caught up with the source, so you can switch traffic based on your migration plan.
   2	Configure Alerts	When the task fails, the system notifies the selected channel through the configured alert.
   3	More	Pause: Pause the task. Only tasks with Running status are selectable. Duplicate: Create a new replication task with the same configuration as the current task. Terminate: Terminate tasks that are incomplete or still listening (that is, in incremental synchronization). After a task is terminated, it cannot be restarted, so proceed with caution. If the synchronization objects contain triggers, trigger replication options appear for selection. Delete: Delete the task. Once deleted, it cannot be recovered, so proceed with caution.
   4	Structure Replication (displayed in scenarios involving structure replication)	Displays the progress and detailed information of structure replication. Click Log to view the execution logs of structure replication. Click the to view the latest information. Click View DDL in the Actions column for the target object in the list to view SQL replay.
   5	Full Replication (displayed in scenarios involving full replication)	Displays the progress and detailed information of full replication. Click Monitor to view various monitoring indicators during full replication. During full replication, you can also click Flow Control Settings on the monitoring page to limit the rate of writing to the target data source per second. The unit is rows/second. Click Log to view the execution logs of full replication. Click the to view the latest information.
   6	Incremental Replication (displayed in scenarios involving incremental replication)	Displays incremental replication indicators. Click View Threads to view the operations currently being executed by the current replication task, including: Thread ID: Replication tasks are executed in multiple threads, and this shows the current thread number. Execute SQL: Details of the SQL statement currently being executed by the current thread. Response Time: The response time of the current thread. If this value increases, it indicates that the current thread may be stuck for some reason. Event Time: The timestamp when the current thread was started. Status: The status of the current thread. Click Flow Control Settings to limit the rate of writing to the target data source per second. The unit is rows/second. Click Log to view the execution logs of incremental replication. Click the to view the latest information.
   7	Modify Object	Displays the modification records of synchronization objects. Click Modify Objects to configure the synchronization objects. Click the to view the latest information.
   8	Data Comparison	Displays the comparison results between the source and target data sources. If data comparison is not enabled, click Enable Comparison on the page to enable it. Click Re-compare to rerun the comparison for the current source and target data sources. Click Stop to stop the comparison task immediately after it starts. Click Log to view the execution logs of consistency comparison. Click Monitor (displayed only in data comparison) to view the trend chart of RPS (records per second) comparison. Click Details to view earlier records. Click the in the Actions column in the comparison list (displayed under the Data tab only when inconsistencies are found) to view details of the comparison between the source and target data sources. Click the in the Actions column in the comparison list (displayed only when inconsistencies are found): Generate change SQL. You can copy this SQL to the target data source and run it to fix the mismatch.
   9	Expand	Displays detailed information of the current replication task. Common actions: Export table configuration: Export the current task's database and table configuration so you can quickly import it when creating another replication task with the same objects. Alert Rules: Configure alerts for the current task.

Appendix: Pre-check items

Check Item	Check Content
Source data source connection check	Check the gateway status of the source data source, whether the instance is reachable, and whether the username and password are correct
Target data source connection check	Check the gateway status of the target data source, whether the instance is reachable, and whether the username and password are correct
Target database permission check	Check whether the target account has the required permissions
Source database permission check	Check whether the source account has the required permissions
Target data existence check	Check whether data already exists in the target objects to be synchronized
Target same-name object existence check	Check whether objects with the same name already exist in the target database
Check wal_level	Check whether wal_level is set to logical on the source
Check max_wal_senders	Check whether max_wal_senders meets the replication connection requirement
Check max_replication_slots	Check whether max_replication_slots meets the replication slot requirement

Related documents

Introduction to Data Replication