Understanding Change Data Capture (CDC) in MySQL and PostgreSQL: BinLog vs. WAL + Logical Decoding

Change Data Capture (CDC) is a powerful tool for transmitting data changes from relational databases like MySQL and PostgreSQL in real-time. CDC enables data replication and transfer, minimizing the impact on source systems and ensuring timely consistency across downstream data stores. There are two ways to track changes in a database: query-based CDC and log-based CDC, which utilizes the database's transaction log. MySQL uses a binary log to record changes, which can operate in three formats: row-based, statement-based, and mixed. PostgreSQL, on the other hand, relies on a Write-Ahead Log (WAL) for replication and recovery. The key difference between MySQL and PostgreSQL lies in how changes are captured and replicated, with MySQL using logical replication and PostgreSQL using physical replication. PostgreSQL introduced logical decoding in version 9.4, which extracts a detailed stream of database changes from the WAL in a human-readable format. CDC tools like Debezium CDC connectors can leverage these logs to perform incremental replication to downstream systems. Understanding how transaction logs work in MySQL and PostgreSQL provides valuable insights into how CDC tools perform real-time data streaming. By leveraging logical decoding, CDC tools can stream real-time data changes from PostgreSQL to downstream systems.