Design a multi-tenant quota system

Q: Design a multi-tenant quota system

This is a System Design interview question from Snowflake for Software Engineer roles. View the full question and solution on PracHub.

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Question

Design a Global Multi-Tenant Quota Service (Single Global Quota per User)

Context

Multiple upstream products (e.g., Drive, Photos) share a single global storage quota per user (e.g., 100 GB per user). The quota service must prevent overdrafts at all times while serving millions of daily active users and QPS across regions.

Functional Requirements

Consume quota.
Release quota.
Optionally query current quota state.

Non-Functional Requirements

Never allow overdraft at any time.
High consistency and high availability.
Low latency where possible.
Scale to millions of DAU and QPS.

Design Prompts

Define APIs (consume, reserve, confirm, release, query) and idempotency.
Choose storage and data model; justify ACID needs.
Describe read/write paths and replication/ack strategy to prevent double-spend.
Handle concurrency across services/regions and race conditions.
Model quota states (Available, Reserved with TTL, Occupied) and timeout/recovery.
Choose sync vs async for consume/release and failure handling/retries.
Propose sharding and multi-region disaster recovery/failover.
Decide on caching or no-caching and keep it consistent.
Add backpressure/rate limiting and hot-key mitigation.
Outline monitoring, SLOs, and capacity planning.