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Oracle Migration and Synchronization to ClickHouse

NineData Data Replication supports copying data from Oracle to ClickHouse, supporting both schema and full data replication.

Function 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​

  • Both source and target data sources have been added to NineData. For instructions on how to add data sources, please refer to Adding Data Sources.

  • The versions of source and target data sources are as follows:

    Source Data SourceTarget Data Source
    Oracle 11g or aboveClickHouse 20.8 or above

  • If incremental replication is required, ensure the following configurations are set in the source data source:

    • Oracle's log mode is set to ARCHIVELOG mode (by default it is NOARCHIVELOG).

      sqlCopy code
      To verify the current log mode: SELECT log_mode FROM v$database;
      If the log mode is NOARCHIVELOG, perform the following steps:
      1. Shut down the database: SHUTDOWN IMMEDIATE;
      2. Start and mount the database: STARTUP MOUNT;
      3. Execute the command to enable archiving: ALTER DATABASE ARCHIVELOG;
      4. Start the database: ALTER DATABASE OPEN;

    • Supplemental Log has been enabled (not enabled by default).

      sqlCopy code
      To verify if Supplemental Log is enabled: SELECT supplemental_log_data_all allc FROM v$database;
      If it returns NO, execute the command to enable Supplemental Log:
      - ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
      //Enables Supplemental Log at the database level, affecting all tables and columns, and consuming more resources.
      - ALTER TABLE <database_name>.<table_name> ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
      - ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
      //Enables Supplemental Log on specific tables, affecting all columns in that table.

  • The access_management parameter value for the account used to log in to ClickHouse must be 1.

    Configuration Method:

    Open the /etc/clickhouse-server/User.xml configuration file with an editor, find the target user, and add the parameter: <access_management>1</access_management>.

  • The following permissions are required for both the source and target data sources.

    Replication TypeSource Data SourceTarget Data Source
    Full Replication
    • select connect
    • select any dictionary
    • select_catalog_role
    		Permissions related to TABLE (CREATE, CREATE TABLE, ALTER, ALTER COLUMN, DROP, SELECT, INSERT)

Notes​

  • If there are unsigned integer type fields in the source Oracle data source, they will be mapped to Uint type in ClickHouse.

  • Typically, Oracle to ClickHouse replication scenarios need to include schema replication, where the system automatically migrates Oracle table structures to ClickHouse and inserts two system columns into tables involved in replication in ClickHouse. If the replication type does not include schema replication, you need to manually ensure the following:

    • The schema of the data objects involved in ClickHouse data sources replication must be consistent with that of the Oracle data source.

    • Two system columns need to be manually inserted into tables involved in ClickHouse data source replication to record DML operations and Binlog time.

      Column NameData TypeDefault ValueDescription
      _jz_data_signInt8DEFAULT 1Records the type of DML operation to ensure consistency between ClickHouse and Oracle data.
      • INSERT operation: recorded as 1.
      • DELETE operation: recorded as -1.
      • UPDATE operation: split into INSERT and DELETE operations.
      _jz_data_timeStringDEFAULT now()Records the time of Binlog.

      Example:

      lessCopy code
      CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
      (
          ...
          _jz_data_sign Int8 DEFAULT 1 COMMENT 'replication data update sign: add = 1, remove = -1',
          _jz_data_time String DEFAULT now() COMMENT 'replication data update time'
      ) ENGINE = engine

Usage Limitations​

  • Before executing data synchronization, evaluate the performance of both source and target data sources, and it is recommended to perform data synchronization during off-peak hours. Otherwise, initializing full data may consume a certain amount of read-write resources of the source and target data sources, resulting in an increase in database load.
  • It is recommended to ensure that each table in the synchronized objects has a primary key or unique constraint, and column names are unique. Otherwise, duplicate synchronization of the same data may occur.

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 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 in the left navigation pane.

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

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

    Parameter
    		Description
    NameEnter a name for the data synchronization task, using a meaningful name for easy identification and management. Maximum 64 characters.
    SourceThe data source where the synchronized object resides.
    TargetThe data source that receives the synchronized object.
    Target Object NameChoose the case conversion rule for object names migrated from the source to the target.
    • Convert all to Lowercase: Convert all object names to lowercase regardless of the naming convention on the source side.
    • Consistent with Source: Retain the naming convention of the source.
    • Convert all to Uppercase: Convert all object names to uppercase regardless of the naming convention on the source side.
    TypeChoose the content to be copied to the target data source.
    • Schema: Only synchronize the schema of the source data source without synchronizing data.
    • Full: Synchronize all objects and data from the source data source, i.e., full data replication. The switch on the right is for periodic full replication. For more information, please refer to Periodic Full Replication.
    If target table already exists (selected when Schema is selected)
    • Pre-Check Error and Stop Task: Stop the task when a table with the same name is detected during the pre-check phase.
    • Skip and Continue Task: When a table with the same name is detected during the pre-check phase, a prompt is sent, and the task continues. Ignore the same-name table during schema replication. If data replication is also performed, data will be appended to the same-name table without overwriting existing data.
    • Delete Objects and Rewrite: When a table with the same name is detected during the pre-check phase, a prompt is sent, and the task continues. During schema replication, the same-name table in the target database is deleted, and the table structure is re-replicated based on the source database. If data replication is also performed, data will be written to the table after the table structure replication is completed.
    • Keep Schema and Clear Data, then Rewrite (optional when both schema and data replication are performed): When a table with the same name is detected during the pre-check phase, a prompt is sent, and the task continues. During schema replication, the table structure in the target database is retained, and data in the same-name table is cleared when data replication begins, and then copied from the original table again.
    Target Table Exists Data (required when Schema is not selected)
    • Pre-Check Error and Stop Task: Stop the task when data exists in the target table is detected during the pre-check phase.
    • Ignore the existing data and append : When data exists in the target table is detected during the pre-check phase, ignore this part of the data and append other data.
    • Clear the existing data before write: When data exists in the target table is detected during the pre-check phase, delete this part of the data and rewrite it.

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

    Parameter
    		Description
    Replication ObjectsChoose the content to be copied. You can select All Objects to copy all contents of the source database, or select Customized Object, select the content to be copied from the Source Object list, and click > to add it to the Target Object list on the right.

    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, select different operations based on the selected replication type, and then click Save and Pre-Check. If there are updates 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 retrieve the information of the source and target data sources again.

    • Including Schema: Configure the table name after synchronization to the target data source.

    • Excluding Schema: The system automatically selects the same-named database in the target data source. If it does not exist, you need to manually select the target database. The table names and column names in the target database need to be consistent with the synchronized objects. If they are not consistent, you can manually map the table names and column names.

    You can click on Mapping & Filtering on the right side of the page to customize the name of the columns after synchronization to the target data source. In addition, you can set Data Filter to configure filter conditions through comparison expressions. Only data that meets the filter conditions will be synchronized to the target data source. For example, setting the filter condition to emp_no>=10005 means that 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 pre-check. After the pre-check passes, click Launch.

    tip
    • You can check Enable data consistency comparison. After the synchronization task is completed, automatic data consistency comparison based on the source data source is initiated to ensure data consistency on both ends. Depending on your selection of Type, the timing of starting Enable data consistency comparison is as follows:
      • Schema: Initiated after schema replication is completed.
      • Schema + Full, Full: Initiated after full replication is completed.
    • If the pre-check fails, you need to click the Details in the Actions column on the right of the target check item, troubleshoot the reason for the failure, manually fix it, and then click Check Again to execute the pre-check again until it passes.
    • Check items with Warning in Result can be repaired or ignored depending on the specific situation.

  8. On the Launch page, when prompted Launch Successfully, the synchronization task begins. At this point, you can:

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

View Synchronization Results​

  1. Log in to the NineData console.

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

  3. On the Replication page, click on the Task ID of the target synchronization task, and the page description is as follows.

    result_no_incre

    Number
    		Function
    		Description
    1Configure AlertsAfter configuring alerts, the system will notify you in the selected way when the task fails. For more information, please refer to Operational Monitoring Overview.
    2More
    • Pause: Pause the task. Only tasks with the status Running are selectable.
    • Duplicate: Create a new replication task with the same configuration as the current task.
    • Terminate: End tasks that are incomplete or in listening (i.e., in incremental synchronization). After terminating the task, it cannot be restarted, so please proceed with caution. If triggers are included in the synchronization object, trigger replication options will pop up, please choose as needed.
    • Delete: Delete the task. Once the task is deleted, it cannot be recovered, so please proceed with caution.
    3Structural Replication (Displayed in scenarios involving structural replication)Display the progress and details of structural replication.
    • Click on Log on the right side of the page: View the execution log of structural replication.
    • Click on refresh on the right side of the page: View the latest information.
    • Click on View DDL in the Actions column on the right side of the target object in the list: View SQL playback.
    4Full Replication (Displayed in scenarios involving full replication)Display the progress and details of full replication.
    • Click on Monitor on the right side of the page: View various monitoring indicators during full replication. During full replication, you can also click on Flow Control Settings on the right side of the monitoring indicator page to limit the rate of data written to the target data source per second. The unit is rows/second.
    • Click on Log on the right side of the page: View the execution log of full replication.
    • Click on refresh on the right side of the page: View the latest information.
    5Data ComparisonDisplay the comparison results between the source data source and the target data source. If you have not enabled data comparison, click Enable Comparison on the page.
    • Click on Re-compare on the right side of the page: Re-initiate the comparison of data between the current source and target ends.
    • Click on Stop on the right side of the page: After starting the comparison task, you can click this button to stop the comparison task immediately.
    • Click on Log on the right side of the page: View the execution log of consistency comparison.
    • Click on Monitor (only displayed in data comparison): View the trend chart of RPS (records per second compared) for comparison. Click on Details to view records from earlier times.
    • Click on details in the Actions column on the right side of the comparison list (displayed only under the Data tab when there is inconsistency): View detailed comparison between the source and target ends.
    • Click on sql in the Actions column on the right side of the comparison list (displayed only in case of inconsistency): Generate change SQL, which you can directly copy to the target data source to execute and modify the inconsistent content.
    6ExpandDisplay detailed information of the current replication task. Common Options:
    • Export table configuration: 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.
    • Alert Rules: Configure the alarm strategy for the current task.

Appendix 1: Data Type Mapping Table​

CategoryOracle Data TypeClickHouse Data Type
Build-in data typeCHAR [(size [BYTE | CHAR])]STRING
NCHAR[(size)]STRING
VARCHAR2(size [BYTE | CHAR])STRING
NVARCHAR2(size)STRING
CLOBSTRING
NCLOBSTRING
LONGSTRING
NUMBER [(p [, s])]
  • If NUMBER is an integer:
    • Length < 10 → INT32
    • Length > 10 but < 20 → INT64
    • Length > 20 → DECIMAL
  • If NUMBER is not an integer → DECIMAL
  • If NUMBER has the identity auto-increment attribute → INT64
FLOAT [(p)]FLOAT32
DATEDATETIME
BINARY_FLOATFLOAT32
BINARY_DOUBLEFLOAT64
TIMESTAMP [(fractional_seconds_precision)]Clickhouse supports DATETIME64:
  • With time precision → DATETIME64
  • Without time precision → STRING
TIMESTAMP [(fractional_seconds_precision)] WITH TIME ZONE
  • Version ≥ 20.3 → DATETIME64
  • Version < 20.3
    • With time precision → DATETIME
    • Without time precision → STRING
TIMESTAMP [(fractional_seconds_precision)] WITH LOCAL TIME ZONE
  • Version ≥ 20.3 → DATETIME64
  • Version < 20.3
    • With time precision → DATETIME
    • Without time precision → STRING
INTERVAL YEAR [(year_precision)] TO MONTHSTRING
INTERVAL DAY [(day_precision)] TO SECOND [(fractional_seconds_precision)]STRING
RAW(size)STRING
LONG RAWSTRING
BLOBSTRING
User Defined Data TypeBFILESTRING
REFSTRING
User Defined Data TypeVARRAYSTRING
NESTED TABLESTRING
Oracle supplied Data TypeAnyDataSTRING
Spatial Data TypeSDO_GEOMETRYSTRING

Appendix 2: Checklist​

Check ItemCheck Content
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 databse privilege checkCheck whether the account privileges of the source database meet the requirements
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

Introduction to Data Replication

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