MySQL to PolarDB-X

NineData Data Replication supports full data replication and incremental replication from MySQL-compatible data sources to Alibaba Cloud PolarDB-X.

Overview

Use this workflow to migrate MySQL data to PolarDB-X and keep the target data source updated with incremental source changes.

Before you begin

Add the source and target data sources to NineData. For details, see Add Data Source.
The supported MySQL source versions range from 5.1 to 9.0.
The target data source must be Alibaba Cloud PolarDB-X.
The source data source must have Binlog enabled, with the following parameters:
- binlog_format=ROW
- binlog_row_image=FULL
  tip
  If the source data source is a standby database, enable log_slave_updates to capture the complete Binlog.

Restrictions

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

Sign in to the NineData Console.
In the left navigation pane, click Replication > Data Replication.
On the Replication page, click Create Replication.

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.
Target Object Name	Select the case conversion rule for object names after they are migrated from the source to the target. Convert all to Lowercase: Regardless of the naming rule on the source, all target names are lowercase. Consistent with Source: Keep the naming rule of the source. Convert all to Uppercase: Regardless of the naming rule on the source, all target names are uppercase.
Replication Mode	Select the replication mode. Uni-directional: A unidirectional data replication task from the source data source to the target data source. Bi-directional: A bidirectional incremental data replication task between the source and target data sources.
Type	Required when Replication Mode is Bi-directional.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. Incremental: After full synchronization completes, perform incremental synchronization based on the logs of the source data source.The icon is used to configure incremental operation types. Clear the operation types to exclude. Cleared operation types will be ignored during incremental synchronization.
Forward Type	Required when Replication Mode is Bi-directional. Select the forward replication type. Full: Synchronize all objects and data from the source data source, namely full data replication. Incremental: After full synchronization completes, perform incremental synchronization based on the logs of the source data source.The icon is used to configure incremental operation types. Clear the operation types to exclude. Cleared operation types will be ignored during incremental synchronization.
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. 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.
Forward Incremental Started	Required only when Forward 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. 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.
Reverse Type	The replication type from the target data source to the source data source. This parameter is displayed only when Replication Mode is Bi-directional. Only Incremental is supported, and it is selected by default and cannot be disabled.
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.

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.

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.

Other available actions:

Select 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.
Select 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.
Select 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.

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.
  - 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 if required.
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.

View replication results

Sign in to the NineData Console.
In the navigation menu, select Replication > Data Replication.

On the Replication page, click the Task ID of the target synchronization task, and review the task details page.

result_sybase

No.	Function	Description
1	Synchronization 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 available for tasks in the running status. Duplicate: Create a new replication task with the same configuration as the current task. Terminate: End tasks that are incomplete or in listening mode (i.e., incremental synchronization). After terminating the task, it cannot be restarted, proceed with caution. If the synchronization object includes triggers, trigger replication options appear for selection. Delete: Delete the task, the task cannot be recovered after deletion, proceed with caution.
4	Full Replication (displayed in scenarios including full replication)	Displays the progress and detailed information of full replication. Select Monitor to view various monitoring metrics during the full replication process. During the full replication process, 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.
5	Incremental Replication (displayed in scenarios including incremental replication)	Displays various monitoring metrics for incremental replication. Select View Threads to view the operations currently being executed by the replication task, including: Thread ID: The replication task is executed by multiple threads, displaying 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 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.
6	Modify Objects	Displays the modification records of synchronization objects. Select Modify Objects to configure synchronization objects. Select the to view the latest information.
7	Data Comparison	Displays the results of the comparison 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: After the comparison task starts, select this button to stop the comparison task immediately. Select Log to view the execution logs of consistency comparison. Select Monitor (only displayed during data comparison) to view the trend chart of comparison RPS (records compared per second). Select Details to view records from earlier times. Select the in the Actions column in the comparison list (only displayed under the Data tab when inconsistencies are found) to view the comparison details between the source and target data sources. Select the in the Actions column in the comparison list (displayed when inconsistencies are found): Generate change SQL. Copy this SQL to the target data source and run it to fix the mismatch.
8	Expand	Displays detailed information of the current replication task.

Appendix: Precheck items

Check item	What NineData checks
Source table key check	Checks whether the objects to replicate include tables without a primary key or unique key.
Source data source connection check	Checks the source gateway status, instance accessibility, and username and password.
Target data source connection check	Checks the target gateway status, instance accessibility, and username and password.
Source database permission check	Checks whether the source database account has the required permissions.
Source standby log update check	Checks whether `log_slave_updates` is set to `ON` when the source database is a standby database.
Source and target version check	Checks whether the source and target database versions are compatible.
Source Binlog check	Checks whether Binlog is enabled for the source database.
Source Binlog format check	Checks whether the source database `binlog_format` is `ROW`.
Source Binlog row image check	Checks whether the source database `binlog_row_image` is `FULL`.
Cyclic replication check	Checks whether a replication loop exists.
Source read-only status check	Checks whether the source database instance is in read-only mode.

Introduction to Data Replication

MySQL to PolarDB-X

Overview​

Before you begin​

Restrictions​

Procedure​

View replication results​

Appendix: Precheck items​

Related documents​