“Preventing race conditions, deadlocks, and write skews in multi-user concurrent applications using interactive transactions, optimistic locking, and advisory locks.”
In high-concurrency web applications, such as e-commerce inventories, flash sales, seat reservations, or financial ledgers, multiple users often attempt to read and modify the same database records simultaneously.
Without appropriate isolation guarantees, applications suffer from:
PostgreSQL supports three distinct transaction isolation levels:
| Isolation Level | Dirty Read | Non-Repeatable Read | Phantom Read | Serialization Anomaly |
|---|---|---|---|---|
| Read Committed (Default) | Prevented | Allowed | Allowed | Allowed |
| Repeatable Read | Prevented | Prevented | Prevented | Allowed |
| Serializable | Prevented | Prevented | Prevented | Prevented |
Optimistic concurrency control is ideal for read-heavy systems where collisions are rare but catastrophic if unhandled. Each row maintains an incrementing version integer.
1import { PrismaClient } from "@prisma/client";23const prisma = new PrismaClient();45export async function transferFundsSafely(6 accountId: string,7 amount: number,8 expectedVersion: number9) {10 // Update only if version matches the state we read11 const result = await prisma.account.updateMany({12 where: {13 id: accountId,14 version: expectedVersion,15 balance: { gte: amount },16 },17 data: {18 balance: { decrement: amount },19 version: { increment: 1 },20 },21 });2223 if (result.count === 0) {24 throw new Error("CONCURRENCY_CONFLICT: Account state was modified by another transaction.");25 }2627 return { success: true };28}
Prisma ORM provides first-class support for interactive transactions with custom isolation levels:
1import { Prisma } from "@prisma/client";23export async function executeAtomicTransfer(fromId: string, toId: string, amount: number) {4 return await prisma.$transaction(5 async (tx) => {6 // 1. Deduct from sender7 const sender = await tx.wallet.update({8 where: { id: fromId },9 data: { balance: { decrement: amount } },10 });1112 if (sender.balance < 0) {13 throw new Error("INSUFFICIENT_FUNDS");14 }1516 // 2. Credit to receiver17 const receiver = await tx.wallet.update({18 where: { id: toId },19 data: { balance: { increment: amount } },20 });2122 // 3. Create audit transaction log23 const auditLog = await tx.auditLog.create({24 data: {25 fromWalletId: fromId,26 toWalletId: toId,27 amount,28 status: "COMPLETED",29 },30 });3132 return { sender, receiver, auditLog };33 },34 {35 isolationLevel: Prisma.TransactionIsolationLevel.Serializable,36 maxWait: 5000, // 5s timeout waiting for a connection37 timeout: 10000, // 10s transaction run limit38 }39 );40}
Serializable isolation eliminates all concurrency anomalies, but transactions may fail with serialization errors (SQLSTATE 40001). You MUST wrap calls in a retry loop when using Serializable mode.Designing for concurrency from Day 1 ensures that your application scales predictably without silent data corruption. Combine optimistic locking for user-facing mutations and interactive serializable transactions for critical ledger operations.
Full Stack Developer specializing in scalable backend systems, Next.js, TypeScript, PostgreSQL, and distributed architectures.
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