Prisma Read/Write Replica Patterns

Read replicas absorb analytics and list traffic—but replication lag can surprise users who write then immediately read. Prisma dual-client setups need explicit routing rules, not hope.

Dual client setup

@Injectable()
export class PrismaService {
  readonly write = new PrismaClient({ datasources: { db: { url: primaryUrl } } });
  readonly read  = new PrismaClient({ datasources: { db: { url: replicaUrl } } });
}

Inject read for dashboards and exports; write for mutations and transactional flows.

Consistency rules

Document lag tolerance per endpoint in OpenAPI descriptions.

Avoiding connection storms

Size replica pools separately from primary. Burst read traffic should not starve write connections. Monitor pg_stat_replication lag and fail over reads to primary when lag exceeds SLO.

Testing replicas locally

Docker Compose with primary + replica teaches teams replication behavior before production. Seed integration tests against both clients.

Read/write separation is a performance win when consistency expectations are explicit—not assumed.