The answer is to create a second table with a row key of 'timestamp#device_id' using natural timestamp order. This approach directly addresses the need for Bigtable multiple access patterns separate tables, because Bigtable’s sorted row-key structure only supports efficient range scans on the leading key component. The original table optimizes for device-first queries, but the cross-device hourly aggregation requires a time-first key to avoid full-table scans. On the Google Professional Cloud Database Engineer exam, this tests your understanding that Bigtable has no secondary indexes, so you must design separate tables for each distinct access pattern—a common trap is trying to force a single table to serve both queries or assuming you can add an index. A useful memory tip: “One pattern, one table; lead with what you query by.”
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 healthcare analytics company uses Cloud Bigtable to store time-series data from medical devices. The table has a row key of 'device_id#timestamp' where timestamp is stored in reverse order (max - timestamp) so that recent data is at the top. Queries that fetch data for a specific device over a date range are very fast. However, analysts also need to run queries that aggregate data across all devices for a specific hour (e.g., count of readings between 2023-01-01 10:00 and 11:00). These queries are extremely slow because they require scanning all rows. The team must redesign the schema to support both access patterns without duplicating data unnecessarily. What is the best approach?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a second table with row key 'timestamp#device_id' (with timestamp in natural order) to support time-range queries.
Option A is correct. Creating a separate table with a row key of 'timestamp#device_id' allows efficient range scans for a given time period across all devices. This is a common pattern in Bigtable to support multiple access patterns. Option B is not possible (no secondary indexes). Option C is external and not a schema change. Option D (adding nodes) helps throughput but not query efficiency.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 BigQuery to query Bigtable via an external table and run the aggregation there.
Why it's wrong here
This is an external solution, not a schema redesign of the Bigtable table.
✗
Increase the number of Bigtable nodes to improve scan throughput.
Why it's wrong here
Scaling nodes can improve throughput but does not reduce the amount of data scanned; the query still scans all rows.
✗
Add a secondary index on the timestamp column.
Why it's wrong here
Bigtable does not support secondary indexes; row key design is the only access path.
✓
Create a second table with row key 'timestamp#device_id' (with timestamp in natural order) to support time-range queries.
Why this is correct
This provides efficient access for the aggregation query by allowing a range scan over the timestamp.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.
Design and implement database schemas — This question tests Design and implement database schemas — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Create a second table with row key 'timestamp#device_id' (with timestamp in natural order) to support time-range queries. — Option A is correct. Creating a separate table with a row key of 'timestamp#device_id' allows efficient range scans for a given time period across all devices. This is a common pattern in Bigtable to support multiple access patterns. Option B is not possible (no secondary indexes). Option C is external and not a schema change. Option D (adding nodes) helps throughput but not query efficiency.
What should I do if I get this PCDE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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