//www.martinrichards.me/tags/concurrency/ Recent content in Concurrency on Martin C. Richards Hugo en Sat, 17 Jan 2026 10:00:00 +0200 //www.martinrichards.me/post/ledger_p1_optimistic_locking_real_time_ledger/ Sat, 17 Jan 2026 10:00:00 +0200 //www.martinrichards.me/post/ledger_p1_optimistic_locking_real_time_ledger/ <h1 id="optimistic-locking-in-a-double-entry-ledger">Optimistic Locking in a Double-Entry Ledger</h1> <p>Ledgers are a deceptively simple problem to tackle. At a certain scale, leveraging a simple <code>SELECT FOR UPDATE</code> works perfectly well—wrap everything in a transaction, and move on.</p> <p>But the moment you need concurrent writes to the same accounts, hundreds of transactions per second, and real-time balance consistency—everything changes. Suddenly, pessimistic locking becomes your bottleneck. Every read blocks, every write queues, and your payment API starts timing out under load.</p>