Iurii Uses: #PostgreSQL

vatnode — EU VAT Validation API

Developer-first SaaS API for EU VAT validation via VIES with Redis caching, change monitoring, and webhook notifications.

HTPBE? — Has This PDF Been Edited?

SaaS platform for PDF authenticity verification with a public REST API.

B2B quote-to-order flow in Next.js: an RFQ → quote → order state machine, per-deal line items, guarded status transitions, and converting an accepted quote

API key management for a public SaaS: hashing keys at rest, prefix + last-4 display, fail-closed validation, and revocation — plus the scoping, rotation, and

Prevent overselling under concurrent checkouts: reservations vs hard decrements, SELECT FOR UPDATE, deadlock-safe multi-line carts, and the payment window.

Gated B2B pricing in Next.js: per-account price lists, server-side access control so prices never leak to crawlers, and a deal-record data model where every

Subscription billing edge cases Stripe glosses over: proration, dunning, the state machine, cancellation timing, refunds, VAT, and webhook ordering.

Feature flags without LaunchDarkly: a Postgres-backed, ~100-line system with deterministic percentage rollout, per-tenant overrides, and caching.

Semantic search for internal docs with Postgres and pgvector: chunk, embed, and query by meaning so people find the right document, not the exact words.

Idempotency key API design: make POST retries that don't double-charge — Postgres key table, ON CONFLICT claim, response replay, TTL, edge cases.

Stripe to Mollie migration in production: mandates instead of Subscriptions, thin webhooks, no proration, no portal, no Tax. What you rebuild yourself.

Build an internal CRM on Supabase: schema design, RLS policies, Next.js App Router frontend, realtime subscriptions, and an honest look at where the weekend

Multi-tenant SaaS database design: shared schema with RLS, schema-per-tenant, and database-per-tenant — trade-offs, real pitfalls, and when to use each.

Production healthcheck endpoints: liveness vs readiness probes, dependency checks with timeouts, 200 vs 503 logic, Docker and Kubernetes config, and security.

PostgreSQL production patterns: UUID v7, soft deletes, RLS for multi-tenant SaaS, partial and covering indexes, PgBouncer connection pooling, and migration

BullMQ vs pg-boss vs node-cron for Node.js background jobs. Trade-offs between Redis and Postgres queues, retries, deduplication, and production monitoring.

JWT vs sessions vs OAuth for SaaS: token invalidation, mobile clients, refresh token rotation, and a decision matrix to pick the right auth pattern.

Add AI to an existing product without a rebuild. Three integration patterns, how to pick the right one, and what production-ready AI actually demands.

UUID v7 vs v4 in PostgreSQL: why random UUIDs fragment B-tree indexes, how UUID v7 fixes it, benchmarks at 5M rows, and Drizzle ORM migration steps.

40+ point production SaaS checklist: auth, Stripe billing, PostgreSQL, rate limiting, email, monitoring, and security — with honest 8-week build estimates.

Stripe webhook production architecture: idempotency keys in PostgreSQL and Redis, BullMQ queue, signature verification in Next.js App Router — with full

Turborepo monorepo with Next.js and Hono, sharing one set of TypeScript types across frontend and backend.