How to Build Real-Time Data Pipelines with SQL Server CDC and Apache SeaTunnel

#programming #cdc #seatunnel #sql

Change Data Capture (CDC) is a powerful feature in SQL Server that enables real-time data integration by tracking INSERT, UPDATE, and DELETE operations on tables. In this article, we’ll explore how SQL Server CDC works, and how to integrate it seamlessly with Apache SeaTunnel to build efficient, scalable data pipelines for AI-ready systems.

🔍 What is CDC?

Change Data Capture (CDC) is a mechanism that logs changes in SQL Server tables by writing them to system-managed change tables. It captures:

INSERT
UPDATE
DELETE

Compared to traditional polling or trigger-based solutions, CDC offers:

✅ Non-intrusive design (no schema changes)
✅ Low-latency change tracking
✅ Easy downstream integration with Kafka, SeaTunnel, ETL tools

🧠 How CDC Works: Architecture Overview

🔧 Key Components

Component	Description
`cdc.dbo_customer_CT`	Change table storing captured modifications
Capture Job	SQL Agent job that scans the transaction log and parses changes
Cleanup Job	Cleans up old CDC data periodically
LSN (Log Sequence Number)	Log marker for each change, supports resume capability

⚙️ How to Enable CDC in SQL Server

-- Enable CDC for the database
EXEC sys.sp_cdc_enable_db;

-- Enable CDC for a specific table
EXEC sys.sp_cdc_enable_table
  @source_schema = N'dbo',
  @source_name   = N'customer',
  @role_name     = NULL,
  @supports_net_changes = 0;

After enabling, SQL Server auto-generates:

cdc.change_tables: One per source table
cdc.lsn_time_mapping: Timestamp mapping
SQL Agent jobs: cdc.<DBName>_capture and cdc.<DBName>_cleanup

🔗 SeaTunnel Integration with SQL Server CDC

Apache SeaTunnel supports CDC natively through its CDC connector. Here’s a sample configuration:

source {
  SqlServer-CDC {
    plugin_output = "customers"
    username = "sa"
    password = "Y.sa123456"
    startup.mode = "initial"
    database-names = ["column_type_test"]
    table-names = ["column_type_test.dbo.full_types"]
    base-url = "jdbc:sqlserver://localhost:1433;databaseName=column_type_test"
  }
}

SeaTunnel reads from the CDC table and transforms change events into a unified format for downstream processing.

🧾 Example CDC Table Structure

Querying the change table after CDC is enabled:

SELECT * FROM cdc.dbo_customer_CT;

You’ll see fields like:

Field	Description
`__$start_lsn`	Log sequence number where change began
`__$operation`	Operation type (1 = DELETE, 2 = INSERT, 3/4 = UPDATE)
`__$seqval`	Sequence value for ordering
Table columns	Snapshot of the row’s data before/after the change

📊 Comparison: CDC vs Trigger vs Timestamp Polling

Feature	CDC	Trigger	Timestamp Polling
Intrusiveness	None	High	None
Latency	Medium (seconds)	Low (milliseconds)	High (minutes)
Resource Overhead	Medium	High	Medium
Delete Detection	✅	✅	❌
SeaTunnel Compatibility	✅	❌	✅

⚠️ Important Tips

SQL Server Agent must be enabled
Create a dedicated read-only CDC user for best practices
Adjust cleanup retention (default: 3 days):

EXEC sys.sp_cdc_change_job
  @job_type = 'cleanup',
  @retention = 43200 -- 30 days (in minutes)

✅ Conclusion

SQL Server’s CDC mechanism offers a reliable, cost-effective way to track data changes. When paired with Apache SeaTunnel’s real-time data ingestion capabilities, it becomes a powerful combo for building AI-ready data lakes, real-time analytics pipelines, and cross-database synchronization solutions.