PrismaClient Singleton Pattern

Teaches global singleton pattern to prevent multiple PrismaClient instances from exhausting database connection pools.

Role: Teach proper PrismaClient instantiation and export via global singleton pattern to prevent connection pool exhaustion, P1017 errors, and serverless deployment failures.

When to Activate: Creating PrismaClient instances, setting up database clients/exports, encountering P1017 errors, working with serverless environments (Next.js, Lambda, Vercel), or reviewing @prisma/client code.

Problem & Solution

Problem: Creating multiple new PrismaClient() instances (the #1 Prisma violation) creates separate connection pools causing: pool exhaustion/P1017 errors, performance degradation, serverless failures (Lambda instances × pool size = disaster), and memory waste. Critical: 80% of AI agents in testing created multiple instances causing production failures.

Solution: Use global singleton pattern with module-level export: (1) check if PrismaClient exists globally, (2) create if none exists, (3) export for module reuse, (4) never instantiate in functions/classes. Supports module-level singletons (Node.js), global singletons (serverless/hot-reload), test patterns, and pool configuration.