Design the schema for a chat product that supports 1:1 and group conversations, persistent message history, per-user read receipts, and presence. Optimize for the dominant read pattern: 'load the last N messages in a conversation, newest first.'

Design the schema for a catalog that supports products with variants (size, color), nested categories, multi-currency pricing, and per-warehouse inventory. Read-heavy: product detail pages and category listings dominate traffic.

Design the schema for a B2B SaaS where every row belongs to a tenant (workspace). Pick an isolation strategy and justify it. The product has users, projects, and tasks; tenants range from 5 to 50,000 seats.

Design the schema for a Twitter-like service: users follow other users, post short messages, and like posts. Generate each user's home timeline. Discuss fan-out-on-write versus fan-out-on-read for timeline assembly.

Design the schema for a booking system (hotel rooms, restaurant tables, or meeting rooms — pick one). Holds expire after a TTL (Time-To-Live) if the user does not check out. Prevent any two confirmed bookings from overlapping for the same resource.

Design the schema for a URL (Uniform Resource Locator) shortener (bit.ly clone) supporting custom short codes, per-link click analytics, optional expiry, and custom branded domains. Traffic is heavily skewed: 99% reads, 1% writes, with a long tail on click events.

Design the schema for an append-only audit log capturing actor, action, target, and metadata. Retention is 7 years for compliance. The product must answer 'what did user X do' and 'what happened to object Y' both quickly. Writes vastly outnumber reads.

Design the schema for a SaaS billing system: customers subscribe to plans, get billed on a cycle, and may upgrade / downgrade with proration mid-cycle. Failed payments retry on a schedule. Every monetary movement must be auditable.

Design the schema for an Uber-like service: riders request trips, drivers accept them, and the system must find the nearest available drivers to a pickup point in real time. Trip history powers earnings and dispute resolution.

Design the schema for a Zendesk-like support system: customers file tickets, tickets flow through queues, agents work them, and SLAs are tracked per priority. Reports show breached SLAs and agent throughput.