Selected work
Production systems, and what was actually wrong with them.
Each of these was a real system with real users. Where the work is a client's, the description is anonymised and the code is rewritten — the problem and the shape of the fix are real, the identifiers are not.
2026
Backend and database performance
A multi-tenant order and work-management platform (client, anonymised)
A production Rails application where deletes took seven minutes
A template delete that had been timing out against a 30-second request ceiling was reduced from 133,973 queries and 387 seconds to 8,724 ms and 3,099 queries — and, more usefully, the pattern behind a dozen smaller incidents was named and fixed.
- Rails 7
- PostgreSQL 16
- Docker
- AWS Lambda
- Sidekiq
2025 – 2026
Design and implementation
A family of small SaaS products (own work)
Subscription billing where the dangerous bugs point the customer’s way
A billing package where every grant, spend and refund is idempotent by database constraint rather than by timing, webhook replays recover rather than double, and a double-charge path was found and closed before a customer hit it.
- TypeScript
- Cloudflare Workers
- D1
- PayPal
- Hono
For the detail behind any of these, the writing has the measurements.Read it, or email hello@farol.dev.