The answer is to use a separate Cloud SQL instance per tenant. This strategy is appropriate for tenant isolation because it provides the strongest possible data boundary, leveraging the physical separation of compute and storage resources to prevent any cross-tenant data leakage, even at the operating system or file system level. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of trade-offs between isolation strength and operational overhead, often appearing as a trick where a separate database per tenant seems sufficient but fails to guard against resource contention or a compromised hypervisor. A common trap is choosing a separate schema within a single database, which lacks true isolation since a SQL injection in one tenant could query another tenant’s tables. For a memory tip, remember “Instance for Isolation” — when compliance or security demands zero shared risk, a dedicated Cloud SQL instance per tenant is the only foolproof choice.
PCDE Design and implement database schemas Practice Question
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 database engineer is designing a Cloud SQL for MySQL schema for a multi-tenant SaaS application. Each tenant's data is isolated. Which TWO strategies are appropriate for tenant isolation?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a separate database for each tenant.
Option A is correct because creating a separate database per tenant provides strong logical isolation at the schema level, preventing accidental cross-tenant data access. Cloud SQL for MySQL supports multiple databases within a single instance, and this approach leverages native MySQL database boundaries without requiring additional filtering logic. It also simplifies backup and restore operations per tenant.
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.
✓
Create a separate database for each tenant.
Why this is correct
Separate databases provide strong isolation and are easy to manage.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single table with a tenant_id column and enforce filtering in application queries.
Why it's wrong here
This is a shared schema approach; not a true isolation strategy because data is co-located.
✗
Use column-level security to hide tenant data.
Why it's wrong here
Column-level security does not isolate rows.
✓
Use a separate Cloud SQL instance per tenant.
Why this is correct
Provides the highest isolation but higher cost; still a valid strategy.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use row-level security policies to restrict access per tenant.
Why it's wrong here
MySQL does not have built-in row-level security; requires complex views or triggers.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that MySQL supports advanced security features like row-level or column-level security, which are actually available in other database engines like PostgreSQL or SQL Server, leading candidates to incorrectly select options C or E.
Detailed technical explanation
How to think about this question
In MySQL, database-level isolation is achieved by creating separate schemas (databases) under the same instance, each with its own tables and user permissions. This approach aligns with the shared-nothing principle for multi-tenancy, where each tenant's data is physically separated at the storage layer. For high-security SaaS applications, using a separate Cloud SQL instance per tenant (Option D) provides even stronger isolation by dedicating compute and memory resources, but at a higher cost and operational overhead.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Create a separate database for each tenant. — Option A is correct because creating a separate database per tenant provides strong logical isolation at the schema level, preventing accidental cross-tenant data access. Cloud SQL for MySQL supports multiple databases within a single instance, and this approach leverages native MySQL database boundaries without requiring additional filtering logic. It also simplifies backup and restore operations per tenant.
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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Question Discussion
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