A walkthrough of concurrency bugs hidden in seemingly correct SQL code, using a money-transfer example. Starting from a naive implementation, the post progressively reveals three critical issues: lack of atomicity, TOCTOU race conditions, and deadlocks. Each bug is explained with a concrete scenario and a fix is shown. The author concludes that SQL's defaults make it easy to write dangerously incorrect code and proposes a Rust-inspired 'fearless concurrency' alternative where safe behavior is the default.
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