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PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
You are designing a Cloud SQL for PostgreSQL instance for an OLTP application. The application typically handles 500 concurrent connections and the working set is 8 GB. You estimate a buffer pool of 4 GB. What minimum memory allocation should you choose?
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
✓
15 GB
Cloud SQL PostgreSQL recommends max_connections = RAM_MB/16, but this is a soft limit. More importantly, memory must accommodate the working set and buffer pool. With 500 connections, 8 GB working set + 4 GB buffer pool = 12 GB, but PostgreSQL also needs overhead. A safe minimum is 15 GB, but the smallest Cloud SQL tier with >12 GB is 15 GB (e.g., db-custom-2-15360). However, among the options, 15 GB is the only viable choice. Note: max_connections formula suggests 15GB RAM gives ~960 connections, which covers 500.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
12 GB
Why it's wrong here
12 GB is close but does not provide overhead for connections and OS.
- ✓
15 GB
Why this is correct
15 GB provides enough memory for working set, buffer pool, and connection overhead.
- ✗
8 GB
Why it's wrong here
8 GB is insufficient for the working set and buffer pool combined.
- ✗
26 GB
Why it's wrong here
26 GB is more than needed; this would be over-provisioning.
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