PolarDB-X Migration Synchronization to PolarDB-X

Use this page to replicate data from one PolarDB-X instance to another in NineData. The link supports schema, full, and incremental replication.

Before you begin

• The source and target data sources have been added to NineData. For details, see Add Data Source.

• Both the source and target data sources are Alibaba Cloud PolarDB-X. In this document, PolarDB-X covers both PolarDB-X distributed edition and PolarDB-X single-node edition.

• As described in Alibaba Cloud documentation, add the NineData service addresses to the allowlists of both the source and target clusters and open the database port in the security group. If you use public access, make sure the public endpoint is available. For details, see the Alibaba Cloud document Configure cluster whitelists.

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

  Replication Type	PolarDB-X (Source)	PolarDB-X (Target)
  Schema Replication	SELECT	CREATE, ALTER, DROP
  Full Replication	SELECT	SELECT, INSERT, UPDATE, DELETE, CREATE
  Incremental Replication	SELECT, REPLICATION CLIENT, REPLICATION SLAVE	SELECT, INSERT, UPDATE, DELETE, CREATE

• For incremental replication, make sure NineData can read the binary log on the source. As described in Alibaba Cloud documentation, PolarDB-X provides Binlog-based data synchronization capabilities. NineData requires binlog_format=ROW and binlog_row_image=FULL on the source. If the source is a read-only node, enable log_slave_updates as well. For details, see the Alibaba Cloud document Data synchronization tools.

Limitations

• Data replication applies only to user databases in the data source. System databases are not replicated. For example, MySQL system databases such as information_schema, mysql, performance_schema, and sys are not replicated.
• The source account must have SELECT privileges for schema and full data replication, SHOW VIEW privileges for view replication, and REPLICATION CLIENT and REPLICATION SLAVE privileges for incremental replication. The target account must have DML and DDL privileges.
• Before starting data synchronization, evaluate the performance of the source and target data sources. Run synchronization during off-peak hours when possible. Otherwise, full data initialization consumes read and write resources on both data sources and increases database load.
• If the source data source contains views, functions, stored procedures, triggers, or events, the definer information of these objects is changed on the target data source to the account used by the current synchronization task to access the target data source.
• Make sure every table in the synchronization objects has a primary key or unique constraint, and that column names are unique. Otherwise, duplicate rows may be synchronized.
• If triggers exist in the source data source, NineData synchronizes the triggers only after incremental synchronization ends.

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. 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.
   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.

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

   Parameter	Description
   Replication Objects	Select the content to replicate. Select All Objects to replicate all content in the source database, or select Customized Object, select the content to replicate in the Source Object list, and click > to add it to the Target Object list on the right.
   Blacklist	Click Add to add a blacklist record, and select the database or object to add to the blacklist. The selected content will not be replicated. This is used to exclude specific databases or objects when performing full-database replication for Customized Object or Full Instance. Left drop-down list: Select the database name to add to the blacklist. Right drop-down list: Select objects in the corresponding database. Select multiple objects if required. Leave it empty to add the entire database to the blacklist. To add multiple databases to the blacklist, click the Add button below to add another row.

   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: NineData 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.

   Other available 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.

7. On the Pre-check tab, wait for NineData 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:

     • Full: Starts after full replication completes.

   • 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 if required.

8. On the Launch page, the Launch Successfully message appears, indicating that the synchronization task has started. 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.

Results

1. Sign in to the NineData Console.

2. In the navigation menu, select 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. Switch traffic based on your migration plan.
   2	Configure Alerts	When the task fails, NineData 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. Select Log to view the execution logs of structure replication. Select the to view the latest information. Select 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. Select Monitor to view various monitoring indicators during full replication. During full replication, select 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. Select Log to view the execution logs of full replication. Select the to view the latest information.
   6	Incremental Replication (displayed in scenarios involving incremental replication)	Displays incremental replication indicators. Select 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. Select Flow Control Settings to limit the rate of writing to the target data source per second. The unit is rows/second. Select Log to view the execution logs of incremental replication. Select the to view the latest information.
   7	Modify Object	Displays the modification records of synchronization objects. Select Modify Objects to configure the synchronization objects. Select 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, select Enable Comparison on the page to enable it. Select Re-compare to rerun the comparison for the current source and target data sources. Select Stop to stop the comparison task immediately after it starts. Select Log to view the execution logs of consistency comparison. Select Monitor (displayed only in data comparison) to view the trend chart of RPS (records per second) comparison. Select Details to view earlier records. Select 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. Select the in the Actions column in the comparison list (displayed only when inconsistencies are found): Generate change SQL. 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 for quick import when creating another replication task with the same objects. Alert Rules: Configure alerts for the current task.

Appendix: Pre-Check Item List

Check Item	Check Content
Target database data existence check	Check whether the object to be replicated not empty in the target database
Objects with the same name in the target database existence check	Check whether the object to be replicated already exists in the target database
Existence check for the Definer of non-table objects	Check whether the definer of view, trigger, procedure, function, event exists in the target database
Source datasource connection check	Check the status of the gateway of the source datasource, database connectable, and verify the username and password
Target datasource connection check	Check the status of the gateway of the target datasource, database connectable, and verify the username and password
Target databse privilege check	Check whether the account privileges of the target database meet the requirements
Source database privilege check	Check whether the account privileges of the source database meet the requirements
Source and target datasource collation check	Check whether the collations of the source and target databases are compatible
Target datasource trigger check	Check the existence of triggers on the target database
Source database log_slave_updates check	When the source database is a slave, check whether log_slave_updates is ON
Source and target datasource version check	Check whether the source and target database versions are compatible
Check if the source database has Binlog enabled	Check if the source database has Binlog enabled
Source database binlog format check	Check whether the binlog format of the source database is 'ROW'
Source database binlog_row_image check	Check whether the binlog_row_image of the source database is 'FULL'
Source and target datasource time zone check	Check whether the timezones of the source and target databases match
Source and target datasource character set check	Check whether the character set of the source and target databases are compatible
Source and target datasource SQL_MODE check	Check whether the SQL_MODE of the source and target databases are compatible
Source and target datasource case-sensitive check	Check whether the case-sensitive configurations of the source database and the target database are compatible
Source datasource and target datasource explicit_defaults_for_timestamp check	Check whether the explicit_defaults_for_timestamp of the source database and the target database are compatible
Source database procedure and function check	Check that the source database has been granted privileges to obtain the definitions of procedures and functions

Related Documentation

Introduction to Data Replication