Change Data Capture: A Comprehensive Guide
Tags: datacapture
Published: 2024-01-02 08:00:00

**This tutorial will empower you to implement Change Data Capture (CDC), allowing you to actively track and manage data changes within your database environment.**

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### Tools used in this tutorial
[DbVisualizer](https://www.dbvis.com/download/), top rated database management tool and SQL client.

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In this tutorial, we'll take you through the entire spectrum of CDC, starting from its foundational concepts and extending to its practical execution. Whether you're a developer, a dedicated database administrator, or simply someone passionate about data, this comprehensive guide offers you the knowledge and resources to adeptly monitor and manage data alterations within your database environment. Let's plunge into the world of Change Data Capture!

## Prerequisites
 For you to make the most of this tutorial, you'll need:

- **Knowledge of databases:** Access to a database system such as MySQL, PostgreSQL, SQL Server, or Oracle would be very beneficial. This guide will provide examples using MySQL, so having a MySQL server or equivalent will be great.
- **[DbVisualizer](https://www.dbvis.com/):** A database tool that can greatly simplify database management and trigger creation. 
- **Basic SQL Knowledge:** Familiarity with SQL queries, database table creation, and CRUD operations (Create, Read, Update, Delete) will be helpful.

## Introduction to Change Data Capture (CDC)
Change Data Capture, often abbreviated as CDC, is a technique used to identify and capture changes made to data in a database. The primary purpose of CDC is to track modifications, additions, or deletions of data, enabling organizations to maintain an accurate and up-to-date record of their data history.

It is very important in database management because data is the lifeblood of modern businesses, and having a historical record of data changes is crucial for various reasons, including compliance, auditing, analytics, and troubleshooting. CDC allows you to capture these changes efficiently and reliably.

## Benefits of Change Data Capture
CDC offers several benefits, such as:

- **Real-time Insights:** CDC enables you to analyze data changes as they happen, providing timely insights.
- **Efficient Data Synchronization:** CDC aids in synchronizing data between different systems, databases, or environments.
- **Accurate Auditing:** Tracking changes helps maintain a transparent and accountable data history for regulatory compliance.
- **Reduced ETL Load:** CDC can reduce the load on your Extract, Transform, Load (ETL) processes by focusing only on changed data.
- **Faster Issue Resolution:** With a clear record of changes, troubleshooting, and issue resolution become faster and more effective.

## Use Cases of Change Data Capture
Change Data Capture (CDC) offers a versatile set of applications that address various data management challenges. By capturing and tracking data changes, CDC becomes an essential tool in several critical scenarios, enhancing efficiency, accuracy, and decision-making. Let's explore some of the prominent use cases where CDC shines:

- **Data Warehousing:** CDC is essential for maintaining accurate and up-to-date data in a data warehousing environment. By capturing changes from source systems and updating the data warehouse, organizations ensure that business users and analysts have access to the most current information for decision-making and analysis. This enables data-driven insights and reporting based on the latest data.
-** Data Migration:** During data migration projects, whether it's transitioning to a new database platform or consolidating data from multiple sources, CDC is instrumental in ensuring data integrity and consistency. By capturing changes in the source system and applying them to the target system, CDC reduces migration time, minimizes downtime, and ensures that the migrated data accurately reflects the latest changes.
- **Real-time Analytics:** Real-time analytics requires access to the most current data. CDC facilitates this by continuously capturing and delivering data changes to analytical systems. This empowers organizations to respond quickly to market trends, customer behavior, and emerging opportunities. For instance, financial institutions can monitor stock market changes in real time to make informed investment decisions.
-** Maintaining Data Integrity:** Data integrity is crucial for maintaining trust in databases. CDC helps organizations maintain data integrity by tracking changes and providing an audit trail of data modifications. This is particularly vital in industries with regulatory requirements, such as healthcare and finance. CDC ensures that changes are recorded, enabling quick identification of unauthorized modifications and preserving data accuracy.

## Understanding Change Data Capture Mechanisms
Let's take a closer look at the mechanisms that power CDC. By understanding these mechanisms, you'll gain insights into how CDC captures and processes data changes, paving the way for effective implementation. 

### Log-based CDC
Log-based CDC involves capturing changes from the database transaction logs. These logs record every transaction, allowing CDC mechanisms to identify and extract data modifications.

What happens is that when a change (insert, update, delete) is made to a database, the corresponding transaction log entry is created. CDC mechanisms read these logs, interpret the changes, and apply them to a separate CDC repository or system.

Transaction logs store a sequential record of all database activities, including changes to data, metadata, and structural elements. Log records include information about the affected rows, columns, and the type of operation performed.

### Pros and Cons of Log-Based CDC
The **pros** of log-based CDC are:

- It offers near-real-time data capture.
- It has minimal impact on source database performance.
- It supports high transaction volumes.

While its **cons** are:

- Implementation complexity varies across DBMS.
- Requires access to transaction logs, which might be restricted.
- Might not capture historical changes if logs are not retained.

### Trigger-Based CDC
Trigger-based CDC relies on database triggers, which are special procedures executed automatically when specific events occur in the database.

Triggers are set on specific tables to activate when a data change operation (insert, update, delete) occurs. These triggers execute custom logic to capture and transmit the changed data.

When a trigger event occurs, the associated trigger code identifies the affected data and pushes it to a CDC system or repository for further processing.

### Pros and Cons of Trigger-Based CDC
The pros of trigger-based CDC are:

- It offers more control over capturing logic.
- It works across different database systems.
- It can handle complex data transformations.

The cons of trigger-based CDC are:

- It can impact source database performance, especially with high-frequency changes.
- Managing and maintaining triggers can be challenging.
- It may require additional development effort.

### Metadata-Based CDC
Metadata-based CDC centers around alterations to the database schema and metadata. Rather than directly monitoring data modifications, this method captures shifts in the database's structural elements and metadata, offering insights into potential data changes. By observing adjustments to table structures, column attributes, and relationships, metadata-based CDC deduces possible modifications to the data.

### Pros and Cons of Metadata-Based CDC
The pros of metadata-based CDC are:

- Less impact on source database performance.
- Useful when direct access to transaction logs is restricted.
- Can provide insights into potential data changes.

The cons of trigger-based CDC are:

- Not as granular as log-based or trigger-based CDC.
- Limited to changes in metadata.
- Requires careful interpretation of metadata changes.

## Selecting the Right CDC Approach for Your Environment
Selecting the most suitable Change Data Capture (CDC) mechanism is a critical decision influenced by several key factors. Your choice should align with your specific database system, performance expectations, and the frequency of data changes. Each CDC mechanism offers unique advantages that cater to distinct scenarios:

- **Log-based CDC:** Ideal for Real-Time Scenarios: Log-based CDC excels in real-time scenarios where capturing data changes with minimal delay is essential. By tapping into the transaction logs, this approach can swiftly detect and transmit changes as they occur. It is particularly beneficial for applications that demand up-to-the-minute insights, such as financial trading platforms or real-time monitoring systems.
- **Trigger-Based CDC:** Providing Control: Trigger-based CDC offers a high level of control over capturing logic. It is suitable for environments where you need customized handling of data changes. By attaching triggers to specific tables, you can dictate precisely how changes are captured, transformed, and propagated. This mechanism empowers you to implement complex business rules and data transformations, making it valuable for scenarios like data quality control and nuanced ETL processes.
- ** Metadata-Based CDC:** Suited for Limited Access to Logs: Metadata-based CDC steps in when direct access to transaction logs is restricted or impractical. This approach observes changes in the database schema and metadata to deduce potential data modifications. It is particularly useful in situations where you might not have full access to transaction logs due to security constraints or database system limitations. Metadata-based CDC allows you to infer changes indirectly, making it a valuable option for scenarios where other mechanisms might not be feasible.

By carefully evaluating your database system's capabilities, your performance expectations, and the nature of data changes, you can make an informed decision about which CDC mechanism aligns best with your specific use case. Whether you require real-time responsiveness, precise control over data capture, or flexibility in constrained environments, there's a CDC approach tailored to meet your needs.

## Configuring and Enabling CDC in the Database

### 1. Log-Based CDC
For **Log-Based CDC**, start by enabling transaction log capturing within your database system. This ensures that every data-changing operation is meticulously recorded in the transaction logs. Subsequently, set up dedicated CDC agents or connectors that extract and interpret these logs. These agents act as conduits, transferring the captured changes to a designated CDC repository or system for further processing.

### 2. Trigger-Based CDC
In the case of **Trigger-Based CDC**, the process entails creating triggers on the relevant database tables. These triggers automatically activate when a data modification (insert, update, delete) occurs. Within these triggers, you'll define the custom logic required to capture and transmit the altered data. Once triggered, this logic extracts the changed data and propels it towards the CDC repository or system.

### 3. Metadata-Based CDC
For **Metadata-Based CDC**, the focus shifts to monitoring alterations in the database schema and metadata. As tables, columns, and relationships evolve, these changes signify potential data modifications. By actively observing these shifts, you can anticipate and deduce potential changes to the data. Unlike other methods, metadata-based CDC does not capture changes directly; rather, it infers modifications based on metadata alterations.

Adhering to the specific steps aligned with your chosen CDC mechanism ensures a robust implementation that effectively captures and processes data changes for your intended purposes.

## Setting up Trigger-based CDC in MySQL
For this tutorial, we will set up one of the CDC methods; Trigger-base CDC. Let’s explore the query to set up trigger-based CDC in the MySQL database environment:

- Creating the CDC Table:
First, create a table to store the captured changes. This table will hold information about the changes, such as the operation type (insert, update, or delete), the affected table, and the changed data.

```
CREATE TABLE cdc_table (
  change_id INT AUTO_INCREMENT PRIMARY KEY,
  table_name VARCHAR(255),
  operation ENUM('INSERT','UPDATE','DELETE'),
  changed_data JSON,
  timestamp TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
```

- Creating Triggers for Data Changes:
Next, create triggers on the tables you want to track for changes. Here's a generic example of an `employees` table:

```
-- the data capture trigger for insert
@delimiter %%%;
CREATE
TRIGGER cdc_employees_insert
AFTER INSERT ON employees
FOR EACH ROW
BEGIN
INSERT INTO cdc_table (table_name, operation, changed_data)
VALUES ('employees', 'INSERT', JSON_OBJECT('id', NEW.id,'name'
, NEW.name,'salary', NEW.salary));
END;

%%%
@delimiter ; 
%%%

-- the data capture trigger for update
@delimiter %%%;
CREATE
TRIGGER cdc_employees_update
AFTER UPDATE ON employees
FOR EACH ROW
BEGIN
INSERT INTO cdc_table (table_name, operation, changed_data)
VALUES ('employees','UPDATE', JSON_OBJECT('id', NEW.id,'name'
, NEW.name, 'salary', NEW.salary));
END;

%%%
@delimiter ; 
%%%
-- the data capture trigger for delete
@delimiter %%%;
CREATE TRIGGER cdc_employees_delete
AFTER DELETE ON employees
FOR EACH ROW
BEGIN
INSERT INTO cdc_table (table_name, operation, changed_data)
VALUES ('employees', 'DELETE', JSON_OBJECT('id', OLD.id,'name'
, OLD.name, 'salary', OLD.salary));
END;

%%%
@delimiter ; 
%%%
```

In this example, three triggers (`cdc_employees_insert`, `cdc_employees_update`, and `cdc_employees_delete`) are created for the `employees` table.

Each trigger fires after the respective operation (insert, update, delete) occurs on the `employees` table.

The trigger logic inserts corresponding records into the `cdc_table` with information about the change operation and the changed data.
<br />
![Creating a trigger in DbVisualizer.](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/2eyapqcae1x3ou3m57nv.png)
<figure><figcaption>Creating a trigger in DbVisualizer.</figcaption></figure>
<br />
You can also create a trigger using the DbVisualizer interface by right-clicking on your database table and selecting “Create Trigger” as in the image above. 

Then entering insert your trigger code logic in the dialog that pops up and click on “Execute”.
<br />
![Entering the trigger logic in DbVisualizer.](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/tkbu9r2oolo2fkufie8y.png)
<figure><figcaption>Entering the trigger logic in DbVisualizer.</figcaption></figure>
<br />

Capturing Changes:
Once the triggers are set up, any change made to the `employees` table will trigger the appropriate trigger, which, in turn, captures and stores the change information in the `cdc_table`.

![Viewing the CDC table.](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/8flrubh2l98b1j1iv712.png)
<figure><figcaption>Viewing the CDC table.</figcaption></figure>
<br />

Keep in mind that trigger-based CDC can impact database performance, especially with high-frequency changes. Carefully consider the performance implications and test the setup in a controlled environment.
By following these steps, you can successfully implement trigger-based CDC in MySQL to track and store data changes for the specified tables. Remember to adapt the example to match your database schema and requirements.

## Challenges and Limitations of Change Data Capture
Change Data Capture (CDC) offers valuable data tracking and management capabilities, but it also presents specific challenges and limitations that organizations should be aware of:

- Performance Impact:
Implementing CDC mechanisms, such as log-based or trigger-based approaches, can introduce additional overhead on the source database. Frequent capturing and processing of changes may lead to increased resource consumption, potentially affecting overall database performance. Mitigating this impact requires careful resource allocation and performance tuning.

- Data Volume and Storage:
In high-velocity data environments, where changes occur rapidly, the volume of captured data can quickly grow. This influx of data might strain storage resources, leading to higher storage costs. Organizations must implement effective data retention strategies and compression techniques to manage the storage demands of CDC-generated data.

- Latency and Real-time Processing:
Achieving real-time or near-real-time data capture is a goal of CDC, but actual latency can vary. Delays might arise due to network congestion, processing time, or synchronization issues. Organizations relying on immediate data availability must assess the chosen CDC mechanism's capabilities against their latency requirements.

- Complexity in High-Frequency Scenarios:
In scenarios characterized by high-frequency data changes, managing and processing an abundance of changes can become complex. Ensuring the CDC process can handle and scale with the increased workload requires careful planning, distribution of tasks, and robust infrastructure.

- Security and Compliance:
CDC involves capturing and replicating sensitive data changes, which raises security concerns. Organizations must implement robust security measures to safeguard captured data, comply with data protection regulations, and ensure that the CDC process doesn't introduce vulnerabilities.

While Change Data Capture (CDC) offers valuable data tracking and management capabilities, it comes with challenges. These include potential performance overhead, managing data volume and storage, achieving real-time processing, handling complexity in high-frequency scenarios, and ensuring security and compliance. Organizations must strategize and plan to harness CDC's benefits while effectively addressing these limitations.

## Conclusion
Congratulations on completing our comprehensive guide on Change Data Capture (CDC). Throughout this tutorial, we've explored capturing and managing data changes in your database environment, from fundamentals to practical implementation.

An integral part of this journey was DbVisualizer, a powerful tool that streamlined trigger creation and execution. If you haven't already, we encourage you to explore DbVisualizer's capabilities for smoother CDC implementation.

CDC plays a vital role in modern data management, providing historical accuracy, compliance support, and efficient data workflows. As you continue, adapt CDC mechanisms to your organization's needs.

Stay engaged with the evolving CDC landscape, and consider how tools like DbVisualizer can enhance your data management. With CDC and DbVisualizer, you're well-equipped for successful data tracking and management. Happy exploring and happy data tracking!

## FAQ (Frequently Asked Questions)

### What is Change Data Capture (CDC), and how does it work?
Change Data Capture (CDC) is a method to track and record changes in a database, achieved through log-based, trigger-based, or metadata-based mechanisms.

### How can I implement CDC in MySQL using triggers?
To implement CDC in MySQL, you'll set up triggers on relevant tables to automatically capture and store data changes in a designated CDC table.

### What are the benefits of Change Data Capture (CDC) in databases?
CDC provides real-time insights, efficient data synchronization, accurate auditing, reduced ETL load, and quicker issue resolution.

### What are the use cases of Change Data Capture (CDC)?
CDC is used for data warehousing, data migration, real-time analytics, and maintaining data integrity.

### What challenges can arise with Change Data Capture (CDC) implementation?
Implementing CDC can impact performance, create data volume and latency issues, introduce complexity, and raise security concerns.


## About the author
Ochuko Onojakpor is a full-stack Python/React software developer and freelance Technical Writer. He spends his free time contributing to open source and tutoring students on programming in collaboration with Google DSC.