01Overview
Every financial change is an immutable event. Projections are pure functions of the event log; rebuilding a corrupted projection takes a single CLI command.
Powers the billing pipeline for a multi-tenant SaaS doing eight-figure ARR.
02The Problem
A row-level mutation in the existing billing schema once cost a four-day forensic audit. Never again.
03Approach
- Append-only event log in PostgreSQL with optimistic concurrency on aggregate version.
- Deterministic, replayable projections for the read side.
- Generated invoices are signed and stored as content-addressed PDFs.
04Outcome
Closed the books 6 days faster every month.
Two financial audits passed without a single follow-up question.