Maxim Mironjuk
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January 17, 2026
A network timeout when calling a payment or order API says nothing about whether the write actually failed on the server. A naive retry mechanism therefore risks duplicate charges, duplicate orders, or duplicate notifications. An idempotency key solves this problem not in application logic but structurally at the database level, with a UNIQUE constraint that reliably prevents duplicate processing even when the same request arrives in parallel. This article shows the practical table design, response snapshots, and a clean cleanup strategy.