Google PCA Practice Question: Analysing and Optimising Technical and Business Processes
A company has a Bigtable instance handling time-series data. Write throughput is below expectations and latency is high. The row key format is `userid_timestamp`. Which row key design change would MOST improve performance?
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 hash of the userid as the row key prefix
Bigtable performance relies on distributing writes across tablets. A row key with a high-cardinality prefix (e.g., hashed userid) avoids hotspots. A timestamp prefix causes all writes to go to the last tablet (hotspot). Reversing timestamp helps but still not as good as hashing. Adding column families does not affect row key distribution.
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 `timestamp_userid` without reversal
Why it's wrong here
This causes all new writes to a single tablet, creating a hotspot.
- ✗
Add more column families to store different metrics
Why it's wrong here
Column families affect storage but not write distribution.
- ✓
Use a hash of the userid as the row key prefix
Why this is correct
Hashing distributes writes evenly across tablets.
- ✗
Reverse the timestamp and use `timestamp_userid`
Why it's wrong here
Reversing timestamp helps but still may cause hotspotting if many writes happen at same time; hashing is better.
Go deeper
Related to this question
Learn chapter
Cloud SQL and Managed Data Stores
Key term
Throughput
Throughput is the rate at which data is successfully transferred from one point to another over a network, typically measured in bits per second.
Key term
Column
A column is a vertical set of values in a database table that stores one specific type of attribute for every row.
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This PCA 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 PCA exam.