For years, MySQL users working with Change Data Capture (CDC), and replication environments have dealt with a fundamental architectural limitation: foreign keys were handled by the Storage Engine (InnoDB) and cascading operations were invisible to the binary log. MySQL 9.6, released January 20, 2026, addresses this long-standing issue by moving foreign key enforcement from the InnoDB storage engine to the SQL layer.
This post examines the technical details of this change, its implications for replication and CDC pipelines such as Readyset, the backward compatibility considerations, and who stands to benefit most from this architectural shift.
The Problem: Storage Engine-Level FK Enforcement
To understand why this change matters, we need to examine how MySQL has historically handled foreign key constraints.
When InnoDB implemented foreign key support, it did so entirely within the storage engine layer. The SQL engine would issue a DELETE or UPDATE statement against a parent table, and InnoDB would internally handle any cascading operations defined by ON DELETE CASCADE or ON UPDATE CASCADE clauses. This design had a critical consequence: the SQL layer never saw these cascaded changes.
Consider this schema:
CREATE TABLE orders ( id INT PRIMARY KEY, customer_id INT, total DECIMAL(10,2) ) ENGINE=InnoDB; CREATE TABLE order_items ( id INT PRIMARY KEY, order_id INT, product_name VARCHAR(100), quantity INT, FOREIGN KEY (order_id) REFERENCES orders(id) ON DELETE CASCADE ) ENGINE=InnoDB;
With data:
INSERT INTO orders VALUES (1, 100, 250.00); INSERT INTO order_items VALUES (1, 1, 'Widget', 5); INSERT INTO order_items VALUES (2, 1, 'Gadget', 3);
When you execute :
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