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Oracle to ClickHouse

NineData Data Replication supports schema replication and full replication from Oracle to ClickHouse.

Overview​

Use Oracle to ClickHouse replication to move Oracle table structures and data into ClickHouse for analytical workloads. Review the ClickHouse account, schema, and system-column requirements before you create the task.

NineData data replication supports schema, full data, and incremental data replication between data sources. For supported data sources, it also supports bidirectional replication for geo-distributed active-active architectures.

  • Schema replication: Replicates object structures between homogeneous and heterogeneous data sources.
  • Full data replication: Uses data sharding and row-level concurrent batch replication to improve throughput. Breakpoint resume helps preserve data accuracy, including for tables without primary keys.
  • Incremental data replication: Replicates DML and DDL changes for supported object types. Row-level concurrency and hotspot merge processing help maintain replication throughput.
  • Bidirectional real-time data replication (only between MySQL instances): Replicates changes in both directions between nodes so data can stay current across participating nodes.

Use these capabilities for full or incremental data replication, migration, synchronization, data integration, and low-downtime migration workflows.

Before you begin​

  • Add the source and target data sources to NineData. For instructions, see Add Data Source.

  • Make sure the source and target versions meet the following requirements:

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

  • If your replication plan requires Oracle log access, configure the source data source as follows:

    • Set the Oracle log mode to ARCHIVELOG mode. The default mode is NOARCHIVELOG.

      To check the current log mode, run:

      SELECT log_mode FROM v$database;

      If the log mode is NOARCHIVELOG, run the following commands:

      SHUTDOWN IMMEDIATE;
      STARTUP MOUNT;
      ALTER DATABASE ARCHIVELOG;
      ALTER DATABASE OPEN;

    • Enable supplemental logging. It is disabled by default.

      To check whether supplemental logging is enabled, run:

      SELECT supplemental_log_data_all allc FROM v$database;

      If the result is NO, use the command that applies to your scenario:

      ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
      ALTER TABLE <database_name>.<table_name> ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS;
      ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;

      ALTER DATABASE ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS enables database-level supplemental logging and can consume more resources. ALTER TABLE <database_name>.<table_name> ADD SUPPLEMENTAL LOG DATA (ALL) COLUMNS enables supplemental logging for a specific table.

  • The access_management parameter value for the ClickHouse account 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 the source and target data sources.

    Replication TypeSource Data SourceTarget Data Source
    Full Replication
    • select connect
    • select any dictionary
    • select_catalog_role
    		TABLE permissions: CREATE, CREATE TABLE, ALTER, ALTER COLUMN, DROP, SELECT, and INSERT

Notes​

  • If the source Oracle data source contains unsigned integer fields, NineData maps them to UInt types in ClickHouse.

  • Oracle to ClickHouse replication typically includes schema replication. NineData migrates Oracle table structures to ClickHouse and inserts two system columns into the ClickHouse tables involved in replication. If the replication type does not include schema replication, make sure the following requirements are met:

    • The schema of the ClickHouse data objects must be consistent with the Oracle source schema.

    • Manually add two system columns to the ClickHouse tables involved in replication. The columns 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:

      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

Restrictions​

  • Before you run a replication task, assess the performance of the source and target data sources. Run the task during off-peak hours when possible because full initialization consumes read and write resources.
  • Each replicated table should have a primary key or unique constraint, and column names should be unique. Otherwise, duplicate rows may be replicated.

Procedure​

  1. Sign in to the NineData Console.

  2. In the left navigation pane, click Replication > Data Replication.

  3. On the Replication page, click Create Replication.

  4. On the Source & Target tab, configure the fields in the table, and click Next.

    Parameter
    		Description
    NameEnter 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.
    SourceThe data source that contains the objects to synchronize.
    Datahub ProjectSelect the target Datahub Project. Data from the source data source will be written to the specified Project.
    TypeSelect the replication type.
    • Schema: Synchronize only the database and table schemas of the source data source, without synchronizing data.
    • 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.
    Spec (Unavailable only when Schema is selected)The specification of the replication task. A larger specification provides a higher replication rate. Hover over the details icon to view the rate and configuration information of each specification. Each specification shows the available quantity and total quantity. When the available quantity is 0, the specification is grayed out and cannot be selected.
    If target table already exists (Required when Schema is selected)
    • 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 message and continue the task. During schema replication, ignore the table with the same name. If you also perform data replication, data is appended to the table with the same name and existing data is not overwritten.
    • Delete Objects and Rewrite: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, delete the table with the same name in the target database and replicate the table schema again based on the source database. If you also perform data replication, data is written after schema replication completes.
    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.

  5. 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_nameThe source table name of the object to synchronize.
    destination_table_nameThe target table name that receives the synchronized object.
    source_schema_nameThe source schema name of the object to synchronize.
    destination_schema_nameThe target schema name that receives the synchronized object.
    source_database_nameThe source database name of the object to synchronize.
    target_database_nameThe target database name that receives the synchronized object.
    column_listThe list of columns to synchronize.
    extra_configurationAdditional 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.

  6. 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 replace_tablename 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.

  1. 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:

      • Schema: Starts after schema replication completes.
      • Schema+Full: Starts after full replication completes.
      • Full: Starts after full replication completes.

    • 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.

  2. 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​

  1. Sign in to the NineData Console.

  2. In the left navigation pane, select Replication > Data Replication.

  3. On the Replication page, click the Task ID of the target synchronization task. Review the task details page.

    result_no_incre

    Number
    		Function
    		Description
    1Configure AlertsWhen the task fails, NineData notifies the selected channel through the configured alert. For more information, see 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 proceed with caution. If triggers are included in the synchronization object, trigger replication options appear for selection.
    • Delete: Delete the task. Once the task is deleted, it cannot be recovered, so proceed with caution.
    3Structural Replication (Displayed in scenarios involving structural replication)Displays the progress and details of structural replication.
    • Select Log to view the execution log of structural replication.
    • Select the refresh to view the latest information.
    • Select View DDL in the Actions column for the target object in the list to view SQL replay.
    4Full Replication (Displayed in scenarios involving full replication)Displays the progress and details of full replication.
    • Select Monitor to view various monitoring indicators during full replication. During full replication, select Flow Control Settings on the monitoring page to limit the rate of data written to the target data source per second. The unit is rows/second.
    • Select Log to view the execution log of full replication.
    • Select the refresh to view the latest information.
    5Data ComparisonDisplays the comparison results 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 to stop the comparison task immediately after it starts.
    • Select Log to view the execution log of consistency comparison.
    • Select Monitor (only displayed in data comparison) to view the trend chart of RPS (records per second compared) for comparison. Select Details to view records from earlier times.
    • Select the details in the Actions column in the comparison list (displayed only under the Data tab when inconsistencies are found) to view detailed comparison between the source and target data sources.
    • Select the sql in the Actions column in the comparison list (displayed only when inconsistencies are found): Generate change SQL. Copy this SQL to the target data source and run it to fix the mismatch.
    6ExpandDisplays detailed information of the current replication task. Common actions:
    • Export table configuration: Export the current task's database and table configuration for quick import when creating another replication task with the same objects.
    • Alert Rules: Configure alerts for the current task.

Appendix 1: Oracle to ClickHouse data type mapping​

CategoryOracle Data TypeClickHouse Data Type
Built-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 and < 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: Precheck items​

Check itemWhat NineData checks
Source data source connection checkChecks the source gateway status, database connectivity, and username and password.
Target data source connection checkChecks the target gateway status, database connectivity, and username and password.
Target database permission checkChecks whether the target database account has the required permissions.
Source database permission checkChecks whether the source database account has the required permissions.
Target database data existence checkChecks whether target objects already contain data.
Target same-name object checkChecks whether objects with the same names already exist in the target database.