Skip to main content

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.

    SourceTarget
    MySQL 8.0MySQL 8.0
    MySQL 5.7MySQL 8.0, 5.7
    MySQL 5.6MySQL 8.0, 5.7, 5.6
    MySQL 5.5MySQL 8.0, 5.7, 5.6, 5.5
    MySQL 5.1MySQL 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.

:::

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​

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 Incremental task, with a specification of Micro.

  • Tasks with a status of Terminated 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 Spec 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.

  1. Log in to the NineData Console.

  2. Click on Replication > Data Replication in the left navigation bar.

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

  4. On the Source & Target tab, configure according to the table below, and click Next.

    ParameterDescription
    NameEnter the name of the data synchronization task for easy search and management. Please use meaningful names. Up to 64 characters are supported.
    SourceData source where the synchronization object is located.
    TargetData source receiving the synchronized object.
    Replication Mode (MySQL only)Choose the replication mode, available only for replication tasks between MySQL instances.
    • Uni-directional: Unidirectional data replication task from the source data source to the target data source.
    • Bi-directional: Bidirectional incremental data replication task between source and target data sources.
    TypeShown only when Replication Mode is Uni-directional.
    • Schema: Syncs only the schema of the source data source, not the data.
    • Full: Syncs all objects and data from the source data source, i.e., full data replication.
    • Incremental: After full synchronization, performs incremental synchronization based on the source data source's logs. Click the setting 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 Target Table Preparation to select the handling strategy in case of same-named tables or identical data.
    Forward TypeReplication type from the source data source to the target data source, shown only when Replication Mode is Bi-directional. Refer to Type above for available options. Incremental is selected by default and cannot be disabled. Click the setting icon to uncheck certain operation types according to your needs. Once unchecked, these operations will be ignored during incremental synchronization.
    Forward Incremental StartedNeeded to select when Replication Mode is Bi-directional and Forward Type is only Incremental.
    • From Started: Starts incremental replication based on the current replication task start time.
    • Customized 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.
    Reverse TypeReplication type from the target data source to the source data source, shown only when Replication Mode is Bi-directional. Only supports Incremental, and is selected by default and cannot be disabled.
    Support DDL ReplicationWhen performing incremental replication, whether to replicate DDL operations. Shown only when Replication Mode is Bi-directional.
    • Forward replication supported, reverse not supported: 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.
    • Not supported: 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.
    Incremental StartedNeeded to select when Replication Mode is Uni-directional and Type is only Incremental.
    • From Started: Starts incremental replication based on the current replication task start time.
    • Customized 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.
    Target Table Preparation
    • If target table already exists (Select Schema):
      • 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 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.
      • Delete Objects and Rewrite: 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.
      • Keep Schema and Clear Data, then Rewrite (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.
    • Target Table Exists Data (Unselected when Schema is selected):
      • Pre-Check Error and Stop Task: Stop the task when data is detected in the target table during the precheck stage.
      • Ignore the existing data and append : Ignore the data detected in the target table during the precheck stage and append other data.
      • Clear the existing data before write: Delete the data detected in the target table during the precheck stage and rewrite.

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

    ParameterDescription
    Replication ObjectsChoose what to replicate. You can select All Objects to replicate all contents of the source database, or choose Customized Object, select the items to be replicated in the Source Object list, and click > to add them to the right Target Object list.
    Blacklist (Optional)Click Add 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 Customized Object or Full Instance.
    • 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.

    If you need to create multiple identical replication links, you can create a configuration file and import it when creating a new task. Click Import Config at the top right corner, then click Download Template to download the configuration file template to your local machine. After editing, click Upload to upload the configuration file for batch import.

    Parameter
    		Description
    source_table_nameName of the source table containing the objects to be synchronized.
    destination_table_nameName of the target table receiving the synchronized objects.
    source_schema_nameName of the source schema containing the objects to be synchronized.
    destination_schema_nameName of the target schema receiving the synchronized objects.
    source_database_nameName of the source database containing the objects to be synchronized.
    target_database_nameName of the target database receiving the synchronized objects.
    column_listList of columns to be synchronized.
    extra_configurationAdditional configuration information can be set here:
    • column_rules: Used to define column mapping and value rules. Field descriptions:
      • column_name: Original column name.
      • destination_column_name: Target column name.
      • column_value: Value to assign, which can be an SQL function or a constant.
    • filter_condition: Used to specify row-level filtering conditions; only rows that meet the criteria will be copied.
    tip

    • An example of the extra_configuration content is as follows:

      {
        "extra_config": {
          "column_rules": [
            {
              "column_name": "created_time", // Original column name to map.
              "destination_column_name": "migrated_time", // Target column name mapped to "migrated_time".
              "column_value": "current_timestamp()" // Change the column value to the current timestamp.
            }
          ],
          "filter_condition": "id != 0" // Only rows where ID is not 0 will be synchronized.
        }
      }

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

  6. On the Mapping 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 Refresh Metadata button in the upper right corner of the page to refresh the information of the source and target data sources.

    • Includes Schema: Configure the table name after synchronization to the target data source. Click Save and Pre-Check.

    • Excludes Schema: 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.

    You can click Mapping & Filtering on the right side of the page to customize the column names after synchronization to the target data source. Additionally, you can set Data Filter, and only data that meets the filtering conditions will be synchronized to the target data source. Taking the test data table employees 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.

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

    tip
    • You can check Enable data consistency comparison. 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 Enable data consistency comparison based on your selection of Type is as follows:
      • Schema: Starts after structural replication is completed.
      • Schema + Full, Full: Starts after full replication is completed.
      • Schema + Full + Incremental, Incremental: Starts when incremental data is first consistent with the source data source and Delay is 0 seconds. You can click View Details to view the synchronization delay on the Details page. sync_delay
    • If the precheck fails, you need to click Details in the Actions column on the right of the target check item, identify the reason for the failure, manually fix it, and then click Check Again to perform the precheck again until it passes.
    • For check items with Result as Warning, you can repair or ignore them based on the specific situation.

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

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

View sync results​

  1. Log in to the NineData Console.

  2. Click on Replication > Data Replication in the left navigation bar.

  3. On the Replication page, click on Task ID for the target synchronization task. The page details are as follows.

    result

    Serial Number
    		Function
    		Description
    1Synchronization DelayThe 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.
    2Configure AlertsAfter 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.
    3More
    • 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.
    4Structural 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 refresh 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.
    5Full 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 refresh on the right side of the page: View the latest information.
    6Incremental Copy (Displayed for scenarios that include incremental copy)Display various monitoring indicators for incremental copy.
    • Click View Threads on the right of the page: View the operations currently being executed by the current copy task, including:
      • Thread ID: The thread number currently in progress for the copy task.
      • Execute SQL: Details of the SQL statement currently being executed by the thread.
      • Response Time: The response time of the current thread. An increase in this value may indicate 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.
    • 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 refresh on the right side of the page: View the latest information.
    7Modify ObjectDisplay the modification records of synchronized objects.
    • Click Modify Synchronized Object on the right of the page to configure synchronized objects.
    • Click refresh on the right side of the page: View the latest information.
    8Data ComparisonDisplay 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 details 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 sql 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.
    9View ReverseDisplayed for bidirectional replication tasks only. Click to view the replication details from the target data source to the source data source.
    10ExpandDisplay detailed information about the current replication task, including Replication Type, Replication Object, Start Time, and more.

Appendix: Checklist of Pre-Check Items​

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

Introduction to Data Replication