PostgreSQL Migration Synchronization to TiDB

NineData data replication supports data synchronization and migration between PostgreSQL and TiDB data sources.

Feature Introduction

NineData data replication supports high-performance replication of structure, full data, and incremental data between data sources. For certain data sources, it also provides bidirectional replication, enabling the quick construction of geo-distributed active-active business architectures.

Structure: Supports the replication of object structures between homogeneous and heterogeneous data sources, greatly reducing the barrier to data replication between two sources.
Full Data: Achieves row-level concurrent batch replication through intelligent data sharding, effectively ensuring replication performance. The independently developed novel breakpoint resume technology ensures the accuracy of data in tables without primary keys.
Incremental Data: Supports DML and DDL incremental data replication for all object types. By leveraging technologies such as row-level concurrency and hotspot merging, it delivers robust replication performance.
Bidirectional Real-time Data Replication (only between MySQL instances): Direct bidirectional replication of data between multiple nodes ensures that all node data remains up-to-date.

With the above features, it is easy and efficient to achieve scenarios such as full|incremental data replication, full|incremental data migration, full|incremental data synchronization, data integration, and seamless migration without downtime, providing enterprises with flexible and reliable data replication solutions.

Prerequisites

The source and target data sources have been added to NineData. For details on how to add them, see Adding Data Sources.
The source database type is PostgreSQL.
The target database is TiDB.

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

Replication Type	Source Data Source	Target Data Source
Structure Replication	CONNECT、SELECT	DDL
Full Replication	CONNECT、SELECT	TABLE-related permissions (ALTER、DROP、SELECT、INSERT、UPDATE、DELETE)
Incremental Replication	SUPERUSER	TABLE-related permissions (ALTER、DROP、SELECT、INSERT、UPDATE、DELETE)

For incremental replication, please open the postgresql.conf file and configure the following parameters. If you cannot find the location of the file, you can execute the SHOW config_file; SQL command in the psql client to view it.
- The wal_level parameter of the source data source must be logical.
- The wal_sender_timeout parameter of the source data source is set to 0. This parameter is used to interrupt replication connections that have been stagnant for more than the specified number of milliseconds. The default value is 60000 milliseconds. Setting it to 0 will disable the timeout mechanism.
- The max_replication_slots parameter of the source data source must be greater than 1. This parameter specifies the maximum number of replication slots that the server can support. The default value is 10.
- The max_wal_senders parameter of the source data source must be greater than 1. This parameter specifies the maximum number of concurrent connections. The default value is 10.

Usage Limitations

Before performing data synchronization, it is necessary to assess the performance of the source and target data sources, and it is recommended to perform data synchronization during off-peak business hours. Otherwise, the initial full data will occupy a certain amount of read and write resources of the source and target data sources, leading to increased database load.
It is necessary to ensure that each table in the synchronization object has a primary key or unique constraint, and the column names have uniqueness, otherwise, the same data may be synchronized repeatedly.

Operation Steps

Commercialization Notice

NineData’s data replication product has been commercialized. You can still use 10 replication tasks for free, with the following considerations:

Among the 10 replication tasks, you can include 1 task, with a specification of Micro.
Tasks with a status of do not count towards the 10-task limit. If you have already created 10 replication tasks and want to create more, you can terminate previous replication tasks and then create new ones.
When creating replication tasks, you can only select the you have purchased. Specifications that have not been purchased will be grayed out and cannot be selected. If you need to purchase additional specifications, please contact us through the customer service icon at the bottom right of the page.

Log in to the NineData Console.
Click on in the left navigation bar.
On the page, click on in the top right corner.

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

Parameter	Description
	Enter the name of the data synchronization task. To facilitate subsequent search and management, please use a meaningful name. Up to 64 characters are supported.
	The data source where the synchronization object is located.
	The data source that receives the synchronization object.
	Select the case conversion rule for object names when migrating from the source to the target. : Regardless of the naming rules on the source side, the naming rules on the target side are all lowercase. : Follow the naming rules on the source side. : Regardless of the naming rules on the source side, the naming rules on the target side are all uppercase.
	Choose the content that needs to be copied to the target data source. : Only synchronize the database table structure of the source data source, without synchronizing the data. : Synchronize all objects and data of the source data source, that is, full data replication. The switch on the right is for periodic full replication. For more information, please refer to Periodic Full Replication. : After the full synchronization is completed, perform incremental synchronization based on the logs of the source data source.
（Required when is selected）	: Stop the task when the same name table is detected during the pre-inspection stage. : Send a prompt and continue the task when the same name table is detected during the pre-inspection stage. During structure replication, ignore the table with the same name. If you also perform data replication, the data will be appended to the table with the same name without overwriting the existing data. : Send a prompt and continue the task when the same name table is detected during the pre-inspection stage. During structure replication, delete the table with the same name in the target database and re-copy the table structure based on the source database. If you also perform data replication, the data will be written after the table structure is copied. （Optional when both structure and data replication are performed）: Send a prompt and continue the task when the same name table is detected during the pre-inspection stage. During structure replication, retain the table structure in the target database, and clear the data in the table with the same name at the beginning of data replication, then re-copy from the original table.
（Required when is not selected）	: Stop the task when data is detected in the target table during the pre-inspection stage. : Ignore the data when it is detected in the target table during the pre-inspection stage, and append other data. : Delete the data when it is detected in the target table during the pre-inspection stage, and rewrite it.

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

Parameter	Description
	Choose the content that needs to be copied. You can select to copy all content from the source database, or you can select , check the content that needs to be copied in the list, and click > to add it to the right list.

If you need to create multiple replication chains with the same replication object, you can create a configuration file and import it when creating a new task. Click on in the top right corner, then click Download Template to download the configuration file template to your local machine, edit it, and then click to upload the configuration file to achieve batch import. Configuration file description:

Parameter	Description
`source_table_name`	The source table name where the object to be synchronized is located.
`destination_table_name`	The target table name that receives the synchronized object.
`source_schema_name`	The source Schema name where the object to be synchronized is located.
`destination_schema_name`	The target Schema name that receives the synchronized object.
`source_database_name`	The source database name where the object to be synchronized is located.
`target_database_name`	The target database name that receives the synchronized object.
`column_list`	The list of fields that need to be synchronized.
`extra_configuration`	Additional configuration information, where you can configure the following information: Column mapping: `column_name`, `destination_column_name` Field value: `column_value` Data filtering: `filter_condition`

tip

An example of extra_configuration is as follows:

{
    "column_name": "created_time", //Specify the original column name for column name mapping
    "destination_column_name": "migrated_time", //Map the target column name to "migrated_time"
    "column_value": "current_timestamp()", //Change the field value of the column to the current timestamp
    "filter_condition": "id != 0" //Only rows with ID not equal to 0 will be synchronized.
}

For the overall example of the configuration file, please refer to the downloaded template.

On the tab, select different operations based on the selected replication type, and then click on . Click on the drop-down menu next to Object Owner to specify the owner of the object, if not selected, the default is . If there are updates in the source and target data sources during the mapping configuration phase, you can click on the button in the top right corner of the page to refresh the information of the source and target data sources.
- Including : Configure the table name after the target table is synchronized to the target data source.
- Not including : The system defaults to selecting the database with the same name in the target data source, if it does not exist, you need to manually select the target library. The table name and column name in the target library need to be consistent with the synchronization object. If they are not consistent, you can also manually map the table name and column name.
You can click on on the right side of the page to customize the name of the column after it is synchronized to the target data source. In addition, you can set , and configure filtering conditions through comparison expressions, only data that meets the filtering conditions will be synchronized to the target data source. For example, if the filtering condition is set to emp_no>=10005, then data with emp_no less than 10005 in the column will not be synchronized to the target data source.
On the tab, wait for the system to complete the pre-inspection, and after the pre-inspection is passed, click on .
tip
- You can check . After the synchronization task is completed, automatically start a data consistency comparison based on the source data source to ensure data consistency on both sides. Depending on the you selected, the timing for starting is as follows:
  - : Start after the structure replication is completed.
  - +, : Start after the full replication is completed.
- If the pre-inspection does not pass, you need to click on in the column on the right side of the target inspection item to investigate the cause of the failure, manually fix it, and then click on to re-execute the pre-inspection until it passes.
- If the is , you can fix or ignore it according to the specific situation.
On the page, it prompts , and the synchronization task starts running. At this point, you can perform the following operations:
- Click on to view the execution of each stage of the synchronization task.
- Click on to return to the task list page.

View Synchronization Results

Log in to the NineData Console.
Click on > in the left navigation bar.

On the page, click on the of the target synchronization task, the page details are as follows.

result

Number	Function	Description
1	Sync Delay	The data synchronization delay between the source data source and the target data source. 0 seconds means there is no delay between the two ends, at which point 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 Operations Monitoring Introduction.
3	More	: Pause the task, only tasks with Running status are selectable. : Create a new replication task with the same configuration as the current task. : End tasks that are unfinished or listening (i.e., in incremental synchronization). Once the task is terminated, it cannot be restarted, so please proceed with caution. If the synchronization objects contain triggers, a trigger replication option will pop up, please select as needed. : Delete the task. Once the task is deleted, it cannot be recovered, so please proceed with caution.
4	Structure Replication (displayed in scenarios involving structure replication)	Displays the progress and detailed information of structure replication. Click on 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 in the column on the right side of the target object in the list: View SQL playback.
5	Full Replication (displayed in scenarios involving full replication)	Displays the progress and detailed information of full replication. Click on on the right side of the page: View various monitoring indicators during full replication. During full replication, you can also click on on the right side of the monitoring indicator page to limit the rate of writing to the target data source per second. The unit is rows/second. Click on 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)	Displays 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: : Replication tasks are executed in multiple threads, displaying 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 indicates that the current thread may be stuck for some reason. : The timestamp when the current thread was started. : The status of the current thread. Click on 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 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	Displays the modification records of synchronization objects. Click on on the right side of the page to configure the synchronization objects. Click on on the right side of the page: View the latest information.
8	Data Comparison	Displays the comparison results between the source data source and the target data source. If you have not enabled data comparison, please click on on the page. Click on on the right side of the page: Re-initiate the comparison between the current source and target data sources. Click on on the right side of the page: After the comparison task starts, you can click this button to stop the comparison task immediately. Click on on the right side of the page: View the execution logs of consistency comparison. Click on (displayed only in data comparison): View the trend chart of RPS (records per second) comparison. Click on to view earlier records. Click on in the column on the right side of the comparison list (displayed under the tab only in the case of inconsistency): View details of the comparison between the source and target sides. Click on in the column on the right side of the comparison list (displayed only in the 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. Common Options: : Export the current task's database and table configuration, allowing for quick import when creating a new replication task. This helps rapidly establish multiple replication links with the same replication objects. : Configure the alarm strategy for the current task.

Appendix: Pre-Check Item List

Check Item	Check Content
Source Data Source Connection Check	Check the gateway status of the source data source, whether the instance is reachable, and the accuracy of the username and password
Target Data Source Connection Check	Check the gateway status of the target data source, whether the instance is reachable, and the accuracy of the username and password
Source Database Permission Check	Check whether the account permissions of the source database meet the requirements
Check wal_level	Check whether the wal_level of the source data source is logical
Check max_wal_senders	Check whether max_wal_senders meets the requirement for the number of replication connections
Check max_replication_slots	Check whether max_replication_slots meets the requirement for the number of replication slots

Introduction to Data Replication

PostgreSQL Migration Synchronization to TiDB

Feature Introduction​

Prerequisites​

Usage Limitations​

Operation Steps​

View Synchronization Results​

Appendix: Pre-Check Item List​

Related Documents​