How Debezium Uses PostgreSQL WAL for Change Data Capture

In the previous article, we looked at how PostgreSQL uses Write-Ahead Logging (WAL) to ensure durability and recover from crashes. But WAL is not just an internal recovery mechanism. Because WAL records every change that happens inside the database, it also enables systems to stream those changes in real time. This is exactly how Change Data Capture (CDC) systems work. Instead of polling tables repeatedly, CDC tools read database changes directly from WAL and turn them into events. One of the most widely used CDC platforms for PostgreSQL is Debezium. In this article, we’ll explore how Debezium reads PostgreSQL WAL and converts database operations into a stream of change events. What is Change Data Capture (CDC) Applications often need to react to changes happening inside a database. For example, imagine a simple update: UPDATE users SET name='Alice Cooper' WHERE id = 1; That change might need to trigger other systems. For example: updating a search i