How a Unique Database Constraint Solves Duplicate Payments in Fintech Systems

·5 views

A developer building a double-entry payments ledger on AWS EKS discovered that handling duplicate 'send money' requests was far harder than managing cloud infrastructure. A naive check-then-insert approach in Python appeared safe but contained a concurrency window where two simultaneous retries could both pass the duplicate check and trigger double debits. The real fix came from a single database-level UNIQUE constraint on the idempotency key, combined with a Postgres ON CONFLICT clause, making deduplication atomic at the storage layer rather than relying on application logic. An ElastiCache layer was added for performance, but only as a cache written after database commit, ensuring Redis failures affect latency rather than financial correctness. The key lesson: sequential tests cannot expose this class of bug, making concurrency-aware design and database-enforced constraints essential in payment systems.

Read the full story at DEV Community

This is an AI-generated summary. ShortSingh links to the original source for the complete article.

Discussion (0)

[Boost]

Agentic Design System sandeep kumar patel Sep 19 Add Comment 1 min read

0 comments Read more at DEV Community

ProgrammingDEV Community ·

AWS Confirms Permanent Data Loss in Middle East Regions After Military Strikes

AWS publicly acknowledged on September 15, 2026, that customer data has been permanently lost across its Bahrain (me-south-1) and UAE (me-central-1) regions following a series of military attacks between March and July 2026. The Bahrain region suffered complete, unrecoverable data loss across all three Availability Zones, while one of three AZs in the UAE region also lost data irretrievably. AWS stated that the destruction spread across multiple Availability Zones, exceeding what its regional and multi-AZ architecture was designed to withstand — effectively acknowledging that multi-AZ redundancy does not protect against large-scale physical warfare. Structural damage, power disruption, and water damage from firefighting operations were cited as key causes of the infrastructure failure. Data lost belonged primarily to customers who had not migrated workloads or maintained backups in other regions before the outages occurred.

0 comments Read more at DEV Community

ProgrammingDEV Community ·

B.Tech Graduate Builds Secure School Portal After 2023 Dehradun Cyber Fraud Case

A recent computer science graduate from Graphic Era Hill University developed a Secure School Management Portal after learning about a 2023 cyber fraud incident in Dehradun, Uttarakhand. In that incident, school manager Shambhu Prasad Pancholi lost ₹95,000 after a fraudster posing as a student's parent sent malicious WhatsApp links that enabled four unauthorized bank transactions. The incident, reported by the Times of India, required no OTP and exploited the manager's trust in a routine fee-payment scenario. Motivated by the case, the developer built a web portal with separate access portals for admins, teachers, and students, incorporating multiple layers of security including authentication and access control. The project, completed as a final-year initiative in 2025, was a personal learning exercise and is not affiliated with the school involved in the original fraud.

0 comments Read more at DEV Community

ProgrammingDEV Community ·

How Runtime Injection Could Bring DLSS Upscaling to Unsupported Legacy Games

A technical concept dubbed DLSS5-Autopilot proposes a method to bring NVIDIA's Deep Learning Super Sampling (DLSS) to older games that never received native support. Rather than requiring game engine modifications, the hypothetical framework operates at the OS driver boundary, intercepting DirectX 12 and Vulkan graphics calls after the game engine has already issued its commands. The system is described as having three layers: an interception layer that hooks GPU API calls, a background inference engine running on Tensor Cores, and a shader hot-swap module that reroutes frames through the DLSS pipeline. This approach targets thousands of AAA titles released between 2015 and 2021 whose closed-source engines make traditional DLSS integration impossible. The article, originally published on tamiz.pro, notes that DLSS5-Autopilot is a hypothetical framework extrapolated from existing NVIDIA driver capabilities and user-space injection techniques, not a released product.

0 comments Read more at DEV Community