Question 776 of 1,446
Design innovative, scalable, and highly available cloud database solutions →mediumMultiple ChoiceObjective-mapped
PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
An engineer is designing a Cloud Spanner schema for a chat application where users send messages. Messages are ordered by timestamp per conversation. The primary key chosen is (ConversationId, MessageId) where MessageId is a monotonically increasing integer. What potential issue might arise with this key design?
⚠ Common exam trap
In Google Cloud Spanner, monotonically increasing keys cause write hotspots because Spanner splits data by key range and sequential inserts target the same tablet, unlike traditional single-node databases where such keys are safe.
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
✓
Writes will be concentrated on a single split causing hotspots.
Using a monotonically increasing integer as the second part of the primary key (MessageId) in Cloud Spanner causes all new writes to be concentrated on a single split (tablet) that handles the highest key range. This creates a hotspot, degrading write throughput and latency, as Cloud Spanner splits data by key range and sequential inserts target the same node.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Queries by conversation will be slow.
Why it's wrong here
Queries by conversation prefix are efficient; the issue is write distribution.
- ✓
Writes will be concentrated on a single split causing hotspots.
Why this is correct
Monotonically increasing keys lead to hotspots in Spanner.
- ✗
The table cannot be interleaved with another table.
Why it's wrong here
Interleaving is still possible.
- ✗
The table will not support secondary indexes.
Why it's wrong here
Spanner supports secondary indexes regardless of primary key design.
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Last reviewed: Jul 4, 2026
This PCDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDE exam.
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