Claude Code
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Race Conditions Causing Data Corruption on Concurrent Updates
When multiple users or processes update the same data simultaneously, your application produces incorrect results. Inventory counts go negative, account balances are wrong, duplicate records appear, or the last write silently overwrites earlier changes without merging them.
Race conditions are among the hardest bugs to find because they're non-deterministic. They happen occasionally under load but almost never during manual testing. You might only discover them when a user complains that their changes disappeared, or when financial totals don't add up.
Claude Code generates code that works correctly for sequential operations but doesn't add concurrency controls. Every read-modify-write sequence without locking is a potential race condition waiting to be triggered under production load.
Error Messages You Might See
ERROR: could not serialize access due to concurrent update
OptimisticLockException: Row was updated by another transaction
Inventory cannot be negative: constraint violation
Duplicate entry for key 'unique_order_id'
StaleObjectStateError: Row was updated or deleted
Common Causes
- Read-modify-write without locking — Code reads a value, modifies it in application code, and writes it back. Between read and write, another request changes the value
- Missing database transactions — Multiple related operations are not wrapped in a transaction, allowing partial completion
- Optimistic concurrency not implemented — No version column or ETag to detect and reject conflicting writes
- Shared mutable state — In-memory counters, caches, or rate limiters modified by multiple async operations without synchronization
- Idempotency not enforced — Retry logic or duplicate requests cause the same operation to execute multiple times
How to Fix It
- Use atomic database operations — Replace read-modify-write with UPDATE counters SET value = value + 1 WHERE id = X
- Add optimistic locking — Include a version column and use UPDATE ... WHERE version = expected_version. Retry on conflict
- Wrap operations in transactions — Use database transactions with appropriate isolation levels (READ COMMITTED or SERIALIZABLE)
- Implement idempotency keys — Accept a client-generated idempotency key and skip duplicate operations
- Use distributed locks for critical sections — For operations spanning multiple services, use Redis-based distributed locks (Redlock)
- Test with concurrent load — Use tools like k6 or Artillery to send concurrent requests and verify data integrity
Real developers can help you.
Matthew Jordan
I've been working at a large software company named Kainos for 2 years, and mainly specialise in Platform Engineering. I regularly enjoy working on software products outside of work, and I'm a huge fan of game development using Unity. I personally enjoy Python & C# in my spare time, but I also specialise in multiple different platform-related technologies from my day job.
Dor Yaloz
SW engineer with 6+ years of experience,
I worked with React/Node/Python
did projects with React+Capacitor.js for ios
Supabase expert
zipking
I am a technologist and product builder dedicated to creating high-impact solutions at the intersection of AI and specialized markets. Currently, I am focused on PropScan (EstateGuard), an AI-driven SaaS platform tailored for the Japanese real estate industry, and exploring the potential of Archify.
As an INFJ-T, I approach development with a "systems-thinking" mindset—balancing technical precision with a deep understanding of user needs. I particularly enjoy the challenge of architecting Vertical AI SaaS and optimizing Small Language Models (SLMs) to solve specific, real-world business problems. Whether I'm in a CTO-level leadership role or hands-on with the code, I thrive on building tools that turn complex data into actionable value.
Krishna Sai Kuncha
Experienced Professional Full stack Developer with 8+ years of experience across react, python, js, ts, golang and react-native. Developed inhouse websearch tooling for AI before websearch was solved : )
Rudra Bhikadiya
I build and fix web apps across Next.js, Node.js, and DBs.
Comfortable jumping into messy code, broken APIs, and mysterious bugs.
If your project works in theory but not in reality, I help close that gap.
Sage Fulcher
Hey I'm Sage! Im a Boston area software engineer who grew up in South Florida. Ive worked at a ton of cool places like a telehealth kidney care startup that took part in a billion dollar merger (Cricket health/Interwell health), a boutique design agency where I got to work on a ton of exciting startups including a photography education app, a collegiate Esports league and more (Philosophie), a data analytics as a service startup in Cambridge (MA) as well as at Phillips and MIT Lincoln Lab where I designed and developed novel network security visualizations and analytics. I've been writing code and furiously devoted to using computers to make people’s lives easier for about 17 years. My degree is in making computers make pretty lights and sounds. Outside of work I love hip hop, the Celtics, professional wrestling, magic the gathering, photography, drumming, and guitars (both making and playing them)
Jaime Orts-Caroff
I'm a Senior Android developer, open to work in various fields
Caio Rodrigues
I'm a full-stack developer focused on building practical and scalable web applications. My main experience is with **React, TypeScript, and modern frontend architectures**, where I prioritize clean code, component reusability, and maintainable project structures.
I have strong experience working with **dynamic forms, state management (Redux / React Hook Form), and complex data-driven interfaces**. I enjoy solving real-world problems by turning ideas into reliable software that companies can actually use in their daily operations.
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Antriksh Narang
5 years+ Experienced Dev (Specially in Web Development), can help in python, javascript, react, next.js and full stack web dev technologies.
Milan Surelia
Milan Surelia is a Mobile App Developer with 5+ years of experience crafting scalable, cross-platform apps at 7Span and Meticha. At 7Span, he engineers feature-rich Flutter apps with smooth performance and modern UI. As the Co-Founder of Meticha, he builds open-source tools and developer-focused products that solve real-world problems.
Expertise:
💡 Developing cross-platform apps using Flutter, Dart, and Jetpack Compose for Android, iOS, and Web.
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Notable Achievements:
🎯 Revamped the Vepaar app into Vepaar Store & CRM with a 2x performance boost and smoother UX.
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Milan is always happy to connect, work on new ideas, and explore the latest in technology.
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Get HelpFrequently Asked Questions
How do I test for race conditions?
Use a load testing tool to send 50-100 concurrent requests that modify the same record. Check if the final state is correct. For example, if 100 requests each increment a counter by 1, the final value should be exactly 100.
What's the difference between optimistic and pessimistic locking?
Optimistic locking allows concurrent reads and detects conflicts at write time (using version numbers). Pessimistic locking prevents concurrent access with database locks. Use optimistic for read-heavy workloads, pessimistic for write-heavy ones.