Overview: Change Data Capture (CDC)
Welcome! In this post, we'll explore Change Data Capture (CDC) — one of those foundational concepts that can genuinely transform the way you think about data synchronization in distributed systems. Let's dive in!
Table of Contents
- What is Change Data Capture?
- Use Cases
- Pros and Cons
- When Should You Use CDC?
- When Should You NOT Use CDC?
- Wrapping Up
What is Change Data Capture?
Change Data Capture (CDC) is a method used in databases to track and record changes made to data.
CDC captures modifications like inserts, updates, and deletes, and makes them available for downstream systems to consume — either for analysis, replication, or synchronization purposes. CDC helps maintain data consistency across different systems by recording alterations in real time.
Think of it like a digital detective sitting quietly inside your database, logging every change that happens and when it occurred — so that other systems never fall behind.
Use Cases
Cache Invalidation
Automatically invalidate entries in a cache as soon as the corresponding record changes or is removed.
If your cache (such as Redis, Memcached, or Infinispan) runs as a separate process, the invalidation logic can be placed into a dedicated service — completely decoupled from your main application. In more advanced setups, you can even use the data from the change event itself to update the affected cache entries directly, rather than just evicting them.
Data Integration
Data is often stored in multiple places, especially when used for different purposes or in slightly different shapes. Keeping those multiple systems in sync can quickly become a maintenance nightmare.
Example: When a system uses a separate search service like Elasticsearch, it's critical to keep the search index synchronized with the primary database whenever records are created or updated.
CDC makes this elegant: changes are captured from the database and automatically propagated to the search service. Instead of sprinkling Elasticsearch update calls throughout your business logic, a lightweight event-processing layer handles it asynchronously. This simplifies the application design while improving scalability and maintainability.
Real-Time Analysis
CDC powers real-time analytics platforms by continuously feeding data changes into analytical systems. Organizations can then derive insights from fresh data and respond swiftly to changing conditions — all without expensive batch jobs or manual ETL pipelines.
Pros and Cons
Pros
1. Decouples Application Logic
- The main application no longer needs to explicitly publish events or sync data to downstream systems.
- Reduces duplicated logic across services — one source of truth emits events, and consumers react independently.
2. Near Real-Time Data Synchronization
- Changes from the database are streamed almost instantly.
- Ideal for search indexing, analytics pipelines, and cache management.
3. Non-Intrusive to Existing Systems
- Works at the database level (via WAL / binlog), so there's usually no need to heavily modify existing application code.
- Particularly useful for integrating with legacy systems where source code changes are risky or costly.
4. Event-Driven Architecture Enablement
- Naturally integrates with streaming platforms like Apache Kafka.
- Makes it easier to build reactive microservices and real-time data pipelines.
5. Data Consistency (Eventually Consistent)
- Ensures downstream systems gradually converge toward the source of truth over time.
- Change events are durable and ordered, making them reliable for replication.
6. Supports Multiple Consumers
- One stream of change events can feed multiple services simultaneously — search indexing, analytics, auditing, cache invalidation, and more.
Cons
1. Increased System Complexity
- Requires additional infrastructure: a message broker (e.g., Kafka), connectors, and monitoring tooling.
- Debugging issues that span multiple components can be significantly harder than debugging a simple API call.
2. Schema Evolution Challenges
- Changes in the database schema (adding/removing columns, renaming tables) can break downstream consumers if not handled carefully.
- A solid schema management strategy — such as a schema registry — becomes essential at scale.
3. Operational Overhead
- Someone needs to manage connectors, track offsets, handle failures, and configure retries.
- This requires a level of DevOps maturity that smaller teams may not yet have.
4. Learning Curve
- Teams need to invest time in understanding event-driven design principles, CDC concepts, and the tooling involved.
- The mental model shift from "call an API" to "react to events" can take time to internalize.
5. Data Filtering and Transformation Are Limited at the Source
- Raw database change events may not perfectly match what downstream consumers need.
- An additional transformation or processing layer is often required to shape, filter, or enrich events before they reach their destination.
When Should You Use CDC?
Use CDC when:
- You need to sync data to systems like Elasticsearch, a data warehouse, or a cache layer
- You are building an event-driven or microservices architecture
- You want to reduce coupling between services
- You need audit logs or historical change tracking
- You have multiple downstream consumers of the same data
- You want near real-time data propagation without modifying core application logic
** Examples:**
- Sync user records from PostgreSQL → Elasticsearch for full-text search
- Stream order events into an analytics pipeline for real-time dashboards
When Should You NOT Use CDC?
Avoid CDC when:
- Your system requires strong consistency — CDC is eventually consistent and introduces some propagation delay
- The system is simple or monolithic and doesn't benefit from event streaming
- You only have one consumer and a direct API call or a database trigger would suffice
- Your team lacks experience in operating distributed systems
- Infrastructure cost and operational complexity are a concern
- Your database is already under heavy load (CDC adds overhead via WAL reading)
Examples:
- A simple CRUD app with basic search — just update Elasticsearch directly from the application
- A low-scale system with no real-time data requirements
Wrapping Up
CDC is a powerful pattern, but like any tool, it shines brightest when applied to the right problem. If you are building systems where data needs to flow reliably across multiple components in near real time, CDC is absolutely worth the investment.
Thank you so much for reading! I hope this overview gave you a clear and practical understanding of Change Data Capture. If you found this helpful, feel free to explore the Debezium setup guide to see how to put these concepts into practice with real infrastructure. Happy building! 🚀
