Data replication between Self-Managed MySQL databases

NineData data replication supports full data synchronization and incremental data synchronization between self-managed MySQL data sources.

Prerequisite

• Added source and target data sources to NineData. For how to add, see Adding Data Sources .

• The versions of the source and target data sources are shown in the table below. Note that the source version must be less than or equal to the target data source version.

  Source	Target
  MySQL 8.0	MySQL 8.0
  MySQL 5.7	MySQL 8.0, 5.7
  MySQL 5.6	MySQL 8.0, 5.7, 5.6
  MySQL 5.5	MySQL 8.0, 5.7, 5.6, 5.5
  MySQL 5.1	MySQL 8.0, 5.7, 5.6, 5.5, 5.1

• The source data source must enable Binlog, and the related parameters of Binlog are set as follows:

  • binlog_format=ROW
  • binlog_row_image=FULL
  tip

  If the source data source is the standby database, in order to obtain the complete Binlog, the log_slave_updates parameter must be turn on.

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Restrictions

• The data replication function is only for the user databases in the data source, and the system databases will not be replicated. For example: information_schema, mysql, performance_schema, sys databases in MySQL type data sources will not be replicated.
• The account for source data must have SELECT (for replicate database structure and full data), SHOW VIEW (for replicate views), and REPLICATION CLIENT, REPLICATION SLAVE (for replicate incremental data) privileges on the objects to be replicated. The account for target must have DML and DDL privileges.
• Before performing data synchronization, user need to evaluate the performance of the source data source and the target data source, and it is recommended to perform data synchronization during off-peak time. Otherwise, the full data initialization will occupy a certain amount of read and write resources of the source data source and the target data source, increasing database load.
• During the synchronization process, if the source data contains views, functions, stored procedures, triggers, and events, after synchronizing to the target data source, the definer of the above objects information will be modified in the target data source to the account that accesses the target data source in the current synchronization task.
• It is necessary to ensure that each table in the synchronization object has a primary key or unique constraint, and the column name is unique, otherwise the same data may be synchronized repeatedly.
• During the synchronization process, if there are triggers in the source, the system will not synchronize the triggers until the incremental synchronization ends.

Steps

1. Log in to the NineData Console.

2. Click on > in the left navigation bar.

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

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

   Parameter	Description
   	Enter the name of the data synchronization task for easy search and management. Please use meaningful names. Up to 64 characters are supported.
   	Data source where the synchronization object is located.
   	Data source receiving the synchronized object.
   (MySQL only)	Choose the replication mode, available only for replication tasks between MySQL instances. : Unidirectional data replication task from the source data source to the target data source. : Bidirectional incremental data replication task between source and target data sources.
   	Shown only when is . : Syncs only the schema of the source data source, not the data. : Syncs all objects and data from the source data source, i.e., full data replication. : After full synchronization, performs incremental synchronization based on the source data source's logs. Click the icon to uncheck certain operation types according to your needs. Once unchecked, these operations will be ignored during incremental synchronization. Note: You can also click to expand to select the handling strategy in case of same-named tables or identical data.
   	Replication type from the source data source to the target data source, shown only when is . Refer to above for available options. is selected by default and cannot be disabled. Click the icon to uncheck certain operation types according to your needs. Once unchecked, these operations will be ignored during incremental synchronization.
   	Needed to select when is and is only . : Starts incremental replication based on the current replication task start time. : Choose the time point to start incremental replication. You can select the time zone according to your business region. If you configure the time point to be before the current replication task start time, the replication task will fail if there are DDL operations during that time period.
   	Replication type from the target data source to the source data source, shown only when is . Only supports , and is selected by default and cannot be disabled.
   	When performing incremental replication, whether to replicate DDL operations. Shown only when is . : Incremental DDL operations in the source data source will be synchronized to the target data source. In this scenario, do not perform DDL operations in the reverse task (target data source), as the task may fail. : All incremental DDL operations will not be synchronized. In this scenario, do not perform DDL operations in either the source or target data source, as the task may fail.
   	Needed to select when is and is only . : Starts incremental replication based on the current replication task start time. : Choose the time point to start incremental replication. You can select the time zone according to your business region. If you configure the time point to be before the current replication task start time, the replication task will fail if there are DDL operations during that time period.
   	(Select ): : Stop the task when a table with the same name is detected during the precheck stage. : When a table with the same name is detected during the precheck stage, display a prompt and continue the task. During structural replication, ignore this same-named table. If you are also replicating data, the data will be appended to the same-named table without overwriting existing data. : When a table with the same name is detected during the precheck stage, display a prompt and continue the task. During structural replication, delete the same-named table in the target database and replicate the table structure based on the source database. If you are also replicating data, the data will be written after the table structure replication is completed. (Selectable when performing both structural and data replication): When a table with the same name is detected during the precheck stage, display a prompt and continue the task. During structural replication, retain the table structure in the target database and clear the data in the same-named table when data replication starts, then replicate from the original table. (Unselected when is selected): : Stop the task when data is detected in the target table during the precheck stage. : Ignore the data detected in the target table during the precheck stage and append other data. : Delete the data detected in the target table during the precheck stage and rewrite.

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

   Parameter	Description
   	Choose what to replicate. You can select to replicate all contents of the source database, or choose , select the items to be replicated in the list, and click > to add them to the right list.
   (Optional)	Click to add a blacklist record, select the databases or objects to be added to the blacklist. These contents will not be replicated. This is used to exclude certain databases or objects in the case of full database replication for or . Left dropdown: Select the name of the database to be added to the blacklist. Right dropdown: Select the objects in the corresponding database. You can click to select multiple objects; leave it blank to add the entire database to the blacklist. If you want to add multiple databases to the blacklist, you can click the Add button below.

6. On the tab, choose different operations 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 synchronization to the target data source. Click .

     tip

     You can click on the right side of the page to customize the column names after synchronization to the target data source. Additionally, you can set , and only data that meets the filtering conditions will be synchronized to the target data source. Using the MySQL official test data "employees" table as an example, if you set the filtering condition to emp_no>=10005, data with emp_no less than 10005 will not be synchronized to the target data source.

   • Excludes : The system automatically selects the same-named database in the target data source, if it exists; otherwise, you need to manually select the target database. The table names and column names in the target database need to match the synchronization objects. If they don't match, you can manually map the table names and column names.

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

   tip

   • You can check . After the synchronization task is completed, automatically start data consistency comparison based on the source data source to ensure data consistency on both ends. The startup timing of based on your selection of is as follows:
     • : Starts after structural replication is completed.
     • + , : Starts after full replication is completed.
     • + + , : Starts when incremental data is first consistent with the source data source and is 0 seconds. You can click to view the synchronization delay on the page. 
   • If the precheck fails, you need to click in the column on the right of the target check item, identify the reason for the failure, manually fix it, and then click to perform the precheck again until it passes.
   • For check items with as , you can repair or ignore them based on the specific situation.

8. On the page, you will receive a prompt , indicating that the synchronization task has started. At this point, you can:

   • Click to view the execution status of the synchronization task at each stage.
   • Click 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 for the target synchronization task. The page details are as follows.

   

   Serial Number	Function	Description
   1	Synchronization Delay	The data synchronization delay between the source data source and the target data source. 0 seconds indicates no delay between the two ends. At this point, you can choose to switch your 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 and Monitoring Introduction.
   3	More	Pause: Pause the task. Only tasks in the Running state can be selected. Terminate: End tasks that are incomplete or in listening mode (i.e., in incremental synchronization). After terminating the task, it cannot be restarted. Please proceed with caution. If the synchronization objects include triggers, trigger replication options will pop up; choose as needed. Delete: Delete the task. Once a task is deleted, it cannot be recovered. Please proceed with caution.
   4	Structural Replication (Displayed for scenarios that include structural replication)	Display the progress and detailed information of structural replication. Click Logs on the right side of the page: View the execution logs of structural replication. Click on the right side of the page: View the latest information. Click View DDL in the Actions column on the right of the target object in the list: View SQL playback.
   5	Full Copy (Displayed for scenarios that include full copy)	Display the progress and detailed information of full copy. Click Monitoring on the right side of the page: View various monitoring indicators during the full copy process. During full copy, you can also click Rate Limit Settings on the right of the monitoring indicator page to limit the rate of writing to the target data source in rows per second. Click Logs on the right side of the page: View the execution logs of the full copy. Click on the right side of the page: View the latest information.
   6	Incremental Copy (Displayed for scenarios that include incremental copy)	Display various monitoring indicators for incremental copy. Click on the right of the page: View the operations currently being executed by the current copy task, including: : The thread number currently in progress for the copy task. : Details of the SQL statement currently being executed by the thread. : The response time of the current thread. An increase in this value may indicate that the current thread may be stuck for some reason. : The timestamp when the current thread started. : The status of the current thread. Click Rate Limit Settings on the right of the page: Limit the rate of writing to the target data source in rows per second. Click Logs on the right side of the page: View the execution logs of the incremental copy. Click on the right side of the page: View the latest information.
   7	Modify Object	Display the modification records of synchronized objects. Click Modify Synchronized Object on the right of the page to configure synchronized objects. Click on the right side of the page: View the latest information.
   8	Data Comparison	Display the results of data comparison between the source data source and the target data source, including Structure Comparison and Data Comparison. If you have not enabled data comparison, click Enable Data Comparison in the page. Click Re-compare on the right side of the page: Re-initiate the comparison of data between the current source and target ends. Click Logs on the right side of the page: View the execution logs of consistency comparison. Click Monitoring (displayed for data comparison only): View the trend chart of RPS (records compared per second) during the comparison. Click Details to view earlier records. Click in the Actions column on the right of the comparison list (displayed on the Data Comparison page only in case of inconsistency): View detailed comparison results between the source and target ends. Click in the Actions column on the right (displayed in case of inconsistency): Generate change SQL. You can copy this SQL directly to the target data source for execution to modify inconsistent content.
   9	View Reverse	Displayed for bidirectional replication tasks only. Click to view the replication details from the target data source to the source data source.
   10	Expand	Display detailed information about the current replication task, including Replication Type, Replication Object, Start Time, and more.

Appendix: Checklist of Pre-Check Items

Check Item	Check Content

Related Documentation

Introduction to Data Replication