https://now-next.nl/en/insights/ Field notes from building two SaaS products with AI agents. Concrete, with the numbers and the miscalculations included. en Mon, 28 Sep 2026 00:00:00 GMT https://now-next.nl/en/insights/invoice-numbers-per-tenant-postgresql-without-gaps/ https://now-next.nl/en/insights/invoice-numbers-per-tenant-postgresql-without-gaps/ Sequence, max()+1, SERIALIZABLE or a counter row: five ways to number invoices per tenant, measured under load in PostgreSQL 17 for duplicates, gaps and speed. Mon, 28 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk https://now-next.nl/en/insights/multi-tenant-postgresql-indexes-tenant-id-first/ https://now-next.nl/en/insights/multi-tenant-postgresql-indexes-tenant-id-first/ Five indexes, 1,000 tenants, one query, measured in PostgreSQL 17: why tenant_id goes first, what RLS does to the plan, and when partitioning pays off. Mon, 28 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk https://now-next.nl/en/insights/multi-tenant-saas-on-postgresql/ https://now-next.nl/en/insights/multi-tenant-saas-on-postgresql/ The six choices a multi-tenant SaaS locks into PostgreSQL: isolation model, RLS, indexes, money, restoring one tenant and migrating at scale. All measured. Tue, 22 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk https://now-next.nl/en/insights/row-level-security-postgresql-tenant-isolation/ https://now-next.nl/en/insights/row-level-security-postgresql-tenant-isolation/ Turning RLS on takes five lines of SQL. These are the five ways it is silently off afterwards, or leaks around the edges — each one measured in PostgreSQL 17. Sat, 19 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk https://now-next.nl/en/insights/money-in-postgresql-numeric-integer-or-money/ https://now-next.nl/en/insights/money-in-postgresql-numeric-integer-or-money/ Which PostgreSQL type holds money exactly? numeric, integer cents, bigint and money side by side, with the pitfalls we tested and a query to audit your schema. Wed, 16 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk https://now-next.nl/en/insights/multi-tenant-architecture-isolation-models/ https://now-next.nl/en/insights/multi-tenant-architecture-isolation-models/ Database per customer, schema per customer or one database with tenant_id and row-level security: the models side by side, and the three questions that decide. Sun, 13 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk https://now-next.nl/en/insights/multi-tenant-from-day-one/ https://now-next.nl/en/insights/multi-tenant-from-day-one/ Three decisions in a SaaS product are nearly impossible to reverse. Separating customers is the first, and the most expensive one to skip. Tue, 01 Sep 2026 00:00:00 GMT SaaS architecture Chris van Eijk