- A
Use separate databases per tenant.
Why wrong: Separate databases increase operational overhead and cost.
- B
Use a single schema with a tenant_id column on every table and row-level security.
Row-level security enforces tenant isolation while keeping a single schema.
- C
Use a single table for all tenants with no tenant identifier.
Why wrong: No isolation at all, compromising data security.
- D
Use a separate Cloud SQL instance per tenant.
Why wrong: Separate instances are expensive and hard to manage.
- E
Use separate schemas per tenant.
Separate schemas provide good isolation and are manageable within a single database.
Question 808 of 1,000
Multi-Tenant Schema Design for Cloud SQL PostgreSQL: Isolate Tenant Data
This PCDE practice question tests your understanding of design and implement database schemas. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A team is designing a Cloud SQL for PostgreSQL schema for a multi-tenant SaaS application. They need to isolate tenant data while maintaining query performance and manageability. Which two approaches are appropriate? (Choose two.)
Quick Answer
The answer is to use separate schemas per tenant and a single schema with tenant_id and row-level security. Separate schemas provide logical isolation within the same database, making backup and restore per tenant straightforward, while row-level security on a shared schema offers fine-grained access control without sacrificing query performance. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of multi-tenant schema design for Cloud SQL PostgreSQL, specifically balancing isolation, cost, and manageability—common traps include choosing separate databases or instances, which are prohibitively expensive for SaaS workloads, or a shared schema with no isolation, which fails the security requirement. Remember the memory tip: “Schema for separation, RLS for sharing”—if you need strict data boundaries, use separate schemas; if you need a shared pool with controlled access, apply row-level security with a tenant_id column.
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 schema with a tenant_id column on every table and row-level security.
Option B is correct because using a single schema with a tenant_id column and row-level security (RLS) in PostgreSQL allows tenant data isolation at the row level while maintaining a single database and schema. RLS policies automatically filter rows based on the current session's tenant context, ensuring performance is optimized through standard indexing on tenant_id and avoiding the overhead of multiple databases or schemas.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 separate databases per tenant.
Why it's wrong here
Separate databases increase operational overhead and cost.
- ✓
Use a single schema with a tenant_id column on every table and row-level security.
Why this is correct
Row-level security enforces tenant isolation while keeping a single schema.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a single table for all tenants with no tenant identifier.
Why it's wrong here
No isolation at all, compromising data security.
- ✗
Use a separate Cloud SQL instance per tenant.
Why it's wrong here
Separate instances are expensive and hard to manage.
- ✓
Use separate schemas per tenant.
Why this is correct
Separate schemas provide good isolation and are manageable within a single database.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google often tests the misconception that separate databases or instances are required for data isolation, but the trap here is that PostgreSQL's row-level security and schema-based isolation (Option E) are both valid and more manageable at scale than physical separation.
Detailed technical explanation
How to think about this question
PostgreSQL row-level security (RLS) works by creating a policy that appends a WHERE clause to every query on the table, using the current_setting('app.tenant_id') or a similar session variable to filter rows. This approach allows fine-grained access control without application-level filtering, and when combined with a composite index on (tenant_id, other_query_columns), it can achieve near-single-tenant performance. In Cloud SQL, RLS is fully supported and can be managed via standard SQL commands like CREATE POLICY, making it a scalable solution for hundreds or thousands of tenants.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCDE question test?
Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a single schema with a tenant_id column on every table and row-level security. — Option B is correct because using a single schema with a tenant_id column and row-level security (RLS) in PostgreSQL allows tenant data isolation at the row level while maintaining a single database and schema. RLS policies automatically filter rows based on the current session's tenant context, ensuring performance is optimized through standard indexing on tenant_id and avoiding the overhead of multiple databases or schemas.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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