Multi-tenancy Study Portal

TL;DR

A multi-tenant system serves many customers (tenants) from one product, and the whole design question is where the wall between tenants lives: in a column every query must filter on, in the database engine, in a schema, in a separate database, or in a separate copy of the whole stack. The further out the wall sits, the stronger the isolation and the higher the cost per tenant. Most real systems start pooled, add a database-enforced safety net, and move their largest or most regulated customers to a silo later. Every model below is described the same way: one plain-words line, where the wall is, pros, cons, who uses it, and sources.