# A Debezium connector against a Postgres logical replication slot has filled the source database disk Canonical URL: Domain: Pipeline Design ยท Difficulty: medium ## Problem A Debezium connector against a Postgres logical replication slot has filled the source database disk twice in the last six months. Each time the connector restarted and never reattached cleanly, and the WAL grew until on-call manually intervened. The section's mechanics: log-based CDC requires an initial snapshot, the slot retains WAL until the consumer confirms read, and stuck consumers cause WAL growth on the source. Place the slot by replacing the Debezium transform with one whose name states the initial snapshot phase, the slot lag monitor (with a budget and an alert threshold), and the schema-evolution policy (additive flows; destructive blocks). ## Related - [All practice problems](https://datadriven.io/problems) - [Mock interview mode](https://datadriven.io/interview/a-debezium-connector-against-a-postgres-logical-replication-f6b5fa97) - [System Design Interview Questions](https://datadriven.io/data-engineering-system-design) - [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep) - [Daily Challenge](https://datadriven.io/daily) --- Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.