Building an Idempotent Refund Flow
The first time a refund double-fired in production, it cost us about 4,200 euros before anyone noticed. A merchant's support agent clicked the refund button,...
10 min814Read →
Articles by Anselm Fowel — page 2
How to Handle a Toxic High Performer
The first time I got this badly wrong, I kept a senior engineer for fourteen months longer than I should have because his throughput was extraordinary. He...
9 min354Read →
The Saga Pattern for Distributed Transactions
A few years ago I watched a payout run leave forty-two merchants with money debited from our settlement account but never credited to their bank. The culprit...
9 min815Read →
Presenting a Technical Roadmap to Executives
The first technical roadmap I ever presented to a board lasted four slides before the CFO stopped me. I was three minutes into explaining why we needed to...
10 min834Read →
Handling Partial Failures in Distributed Systems
A payment either happens or it doesn't. That's the story we tell customers, and it's the story regulators want to hear. But underneath, a single card...
10 min342Read →
Managing a Team That Is Smarter Than You
Early in my time running engineering at a payments company, I sat in a design review for a ledger rewrite and realized, about ten minutes in, that I could not...
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Why We Chose PostgreSQL Over a NoSQL Store
The meeting that decided this ran about forty minutes. We had a greenfield ledger service to build, a payments platform that would eventually touch a few...
10 min585Read →
Why Your Best Ideas Come From Junior Engineers
Three years ago, a graduate engineer named Priya asked me why our payment reconciliation job ran every fifteen minutes. She had been with us for six weeks. The...
10 min810Read →
Designing a Ledger-Backed Wallet System
The first wallet system I inherited stored balances as a single column on the user row. A background job updated it. When two payments landed in the same 200...
9 min771Read →
Urgent vs Important on an Engineering Team
A few years ago I kept a spreadsheet of everything my team shipped in a quarter, and then I ran a quiet little experiment. Next to each item I wrote two...
10 min900Read →
Database Transactions and Isolation Levels, Explained
A few years ago we shipped a payment reconciliation job that, under load, occasionally credited a merchant twice for the same settlement. Not often. Maybe one...
10 min847Read →
Building an On-Call Rotation That Does Not Burn People Out
The pager went off at 3:42 on a Tuesday morning. A payment reconciliation job had stalled, and the alert routed to an engineer who had been on call for eleven...
10 min802Read →