DBS-C01 Workload-Specific Database Design Practice Question
A company is designing a multi-tenant SaaS application on Amazon RDS for PostgreSQL. Each tenant's data must be isolated for security and performance. The application has millions of tenants, with most tenants having small datasets (under 100 MB). Which database design pattern is MOST cost-effective and operationally efficient?
⚠ Common exam trap
Many exam-takers assume separate schemas per tenant (Option C) are the best balance of isolation and cost, but they overlook PostgreSQL's practical limits on the number of schemas and the severe performance degradation from catalog bloat when dealing with millions of tenants.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a single RDS instance with a shared schema and implement Row-Level Security (RLS) policies based on tenant_id.
Using a single RDS for PostgreSQL instance with Row-Level Security (RLS) allows you to isolate tenant data at the row level based on a tenant_id column, without the overhead of managing millions of separate schemas or tables. This design is both cost-effective (single instance, no per-tenant provisioning) and operationally efficient (simple schema management, no connection pooling issues), while still meeting security and performance isolation requirements for small datasets under 100 MB.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use Amazon DynamoDB with a separate table per tenant.
Why it's wrong here
DynamoDB is NoSQL; the application may require relational features, and separate tables for millions of tenants is not scalable.
- ✓
Use a single RDS instance with a shared schema and implement Row-Level Security (RLS) policies based on tenant_id.
Why this is correct
RLS provides tenant isolation with minimal overhead, suitable for many small tenants.
- ✗
Use a single RDS instance with a separate schema per tenant.
Why it's wrong here
Managing millions of schemas in one database is inefficient and can cause performance issues.
- ✗
Use a separate Amazon RDS for PostgreSQL instance per tenant.
Why it's wrong here
This is not cost-effective for millions of small tenants; it would create massive operational overhead and cost.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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