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Db2 to ClickHouse: Build a Continuous Data Pipeline for Analytics

Many enterprises still use Db2 for core business systems, while reporting, business intelligence, and analytical services need a database optimized for aggregation and multidimensional queries.

A one-time export quickly becomes stale. A collection of custom synchronization scripts also leaves schema changes, task failures, and result verification to separate processes. A more manageable approach is to initialize the target first and then keep the target synchronized with subsequent source changes.

NineData currently supports the Db2 -> ClickHouse replication link with schema replication, full replication, incremental replication, column mapping, and data comparison. Initialize historical Db2 data in ClickHouse, continue synchronizing later changes, and provide analytics services with a managed data channel.

Db2 and ClickHouse can serve different roles: Db2 handles transactional workloads, while ClickHouse serves analytical queries. Use a replication task to copy selected Db2 objects to ClickHouse and reduce the impact of analytical queries on the business database.

Typical use cases include:

  • Initializing orders, customers, transactions, or logs in ClickHouse for an independent analytical dataset.
  • Supplying continuously updated data to operational reports, BI dashboards, and subject-area analysis.
  • Preparing a target database before a database migration or architecture change, then validating it before application cutover.
  • Selecting only the required databases, tables, and columns to control the replication scope.

How NineData connects Db2 and ClickHouse​

1. Schema replication: Prepare target objects​

When schema replication is enabled, NineData prepares the target structure in ClickHouse for the selected Db2 objects. This avoids creating target databases and tables one by one. When the source and target structures differ, review the object mapping and configure column mappings if required.

If the target tables already exist in ClickHouse, confirm their structure and decide how existing data should be handled before creating the task. This helps prevent an initialization result that differs from your plan.

2. Full replication: Initialize historical data​

Full replication writes existing Db2 data to ClickHouse. Select the objects that belong to the required business scope and schedule the task based on the resources available on both sides.

After the full phase finishes, ClickHouse has the historical data required for analysis and can continue receiving incremental changes.

3. Incremental replication: Keep later changes synchronized​

When incremental replication is enabled, the task continues processing subsequent data changes from Db2 so that ClickHouse follows the source. Db2 can continue serving the business system while analytical services use the continuously updated data in ClickHouse.

For a migration project with a short cutover window, run full replication first, wait for incremental replication to catch up, and then use data comparison before scheduling the application cutover.

4. Data comparison: Verify the replication result​

After replication, use data comparison to inspect differences between the source and target. The comparison result helps the team find issues before a migration cutover, project acceptance, or routine data-governance review.

Before you begin​

  • Create the Db2 source and ClickHouse target in NineData and verify both connections. For details, see Create a Db2 Data Source and Create a ClickHouse Data Source.
  • Confirm that NineData can access both data sources. For isolated networks, prepare the required gateway, SSH Tunnel, or allowlist configuration in advance.
  • Prepare a Db2 account for reading data and metadata, and a ClickHouse account for writing target objects. Follow the requirements reported by the task precheck for the exact privileges.
  • If ClickHouse requires SSL-encrypted connections, enable SSL when you create the data source and complete the required certificate or connection settings.
  • Decide how existing target objects and data should be handled. This prevents unexpected overwrite, append, or conflict behavior when target tables already exist.

Use one task for initialization and continuous synchronization​

Create a Db2 -> ClickHouse replication task in this order:

  1. Add and test the Db2 source and ClickHouse target data sources.
  2. Create a replication task and select Db2 as the source and ClickHouse as the target.
  3. Select schema, full, and incremental replication based on your migration goal, then choose the databases, tables, and columns to synchronize.
  4. Review object mappings and column mappings, including target object names and the data-handling strategy.
  5. Run the task precheck and resolve connection, privilege, object, or target-data issues reported by the check.
  6. Start the task, monitor its status and replication results, and run data comparison after the task finishes to verify key data.

For detailed procedures, see Create a Data Replication Task.

Keep transactional and analytical workloads in the right place​

Db2 to ClickHouse is more than a one-time export. It combines schema replication, full replication, incremental replication, and data comparison into a continuous data pipeline. The team can initialize historical data first and then keep subsequent business changes moving to the analytical side.

If you are building reports or a BI platform, or moving Db2 data to a target better suited for analytical queries, start with one business subject or a small group of core tables. Verify object mappings, data results, and incremental delay before expanding the replication scope.