Resolving PostgreSQL replication lag with heartbeat tables in change data capture scenarios

This article explains how to resolve PostgreSQL replication lag during change data capture (CDC) migrations using heartbeat tables to prevent Write-Ahead Log (WAL) accumulation.

• Replication slots stall when CDC tasks track only a subset of tables while heavy writes occur elsewhere, causing WAL to accumulate on disk.
• Heartbeat tables generate periodic WAL records to keep replication slots advancing and prevent disk space exhaustion.
• AWS DMS provides built-in heartbeat support via the heartbeatEnable parameter with configurable frequency and schema.
• Debezium implements heartbeats using heartbeat.interval.ms configuration and heartbeat.action.query to write to a dedicated table or emit logical messages.
• Monitor replication health using CloudWatch metrics (OldestReplicationSlotLag, TransactionLogsDiskUsage) or PostgreSQL diagnostic queries on pg_replication_slots.
• Recommended heartbeat frequency ranges from 30 seconds to 5 minutes depending on WAL generation rate and disk constraints.

Implementing heartbeat tables is a lightweight, effective solution to maintain replication slot health and prevent migration delays caused by WAL accumulation.