MySQL Checkpointing for n8n

Idempotency is not optional. Any workflow that can be re-run must produce identical results on the second run. MySQL (or Postgres — patterns are identical) is the pragmatic way.

The three checkpoint tables every pipeline needs

1. processed_items — did we already handle this?

CREATE TABLE processed_items (
  item_key VARCHAR(255) PRIMARY KEY,      -- natural ID (webhook event_id, order_id, etc.)
  workflow_name VARCHAR(100) NOT NULL,
  processed_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  status VARCHAR(20) NOT NULL,            -- 'success' | 'failed' | 'skipped'
  payload_hash VARCHAR(64),               -- SHA256 of payload, detects payload changes
  INDEX idx_workflow_status (workflow_name, status),
  INDEX idx_processed_at (processed_at)
);