- A
Increase the number of cluster nodes to improve compaction
Why wrong: More nodes increase cost and compaction happens automatically.
- B
Use Cloud Storage as a cold storage tier for historical data
Export old data to Cloud Storage and delete from Bigtable.
- C
Enable Bigtable replication and delete data from one cluster
Why wrong: Replication increases storage cost; deleting from one cluster after replication is not standard.
- D
Set garbage collection to delete data older than 30 days
Garbage collection automatically removes old data, reducing storage.
- E
Reduce the number of cluster nodes to save costs
Why wrong: Fewer nodes degrade performance for recent data.
Question 885 of 1,000
Reducing Cloud Bigtable Storage Costs for Time-Series Data — Google PCDE
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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 company runs a Bigtable instance for time-series data. They need to reduce storage costs without compromising query performance for the most recent 30 days. Which three strategies should they implement?
Quick Answer
The correct strategies are to set garbage collection to delete data older than 30 days and to move historical data to Cloud Storage as a cold tier, because Bigtable’s row-based storage is optimized for low-latency queries on recent time-series data, not for long-term retention of stale records. By configuring garbage collection policies with a max age of 30 days, you automatically purge expired cells, reducing storage footprint without affecting scan performance on current data. Meanwhile, exporting older data to Cloud Storage (e.g., in Parquet or Avro format) offloads cold data from Bigtable’s expensive SSD-backed nodes, directly cutting costs while keeping the hot 30-day window fully performant. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of Bigtable’s time-series optimization and lifecycle management—a common trap is assuming that compaction alone reduces storage, but GC policies are required for proactive deletion. Memory tip: “Hot 30, cold 30” — keep 30 days hot in Bigtable, move or delete everything older than 30 days.
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 Cloud Storage as a cold storage tier for historical data
The question asks for three strategies, but among the options provided, only two directly reduce storage costs without compromising query performance for the most recent 30 days: Option B (using Cloud Storage as a cold storage tier for historical data) and Option D (setting garbage collection to delete data older than 30 days). Option B offloads old data to cheaper storage while keeping recent data in Bigtable for fast access. Option D automates deletion of stale data, reducing storage footprint without affecting recent queries. The other options are incorrect: increasing nodes (A) raises costs, replication with deletion (C) risks data loss, and reducing nodes (E) would degrade performance for recent data. Thus, the correct answers are B and D, and the question's mention of 'three' is an error in the source material.
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.
- ✗
Increase the number of cluster nodes to improve compaction
Why it's wrong here
More nodes increase cost and compaction happens automatically.
- ✓
Use Cloud Storage as a cold storage tier for historical data
Why this is correct
Export old data to Cloud Storage and delete from Bigtable.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable Bigtable replication and delete data from one cluster
Why it's wrong here
Replication increases storage cost; deleting from one cluster after replication is not standard.
- ✓
Set garbage collection to delete data older than 30 days
Why this is correct
Garbage collection automatically removes old data, reducing storage.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Reduce the number of cluster nodes to save costs
Why it's wrong here
Fewer nodes degrade performance for recent data.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that reducing cluster nodes or increasing nodes is a direct cost-saving strategy, but candidates must remember that performance requirements (especially for recent data) dictate node count, and cost savings must come from data lifecycle management, not infrastructure scaling.
Detailed technical explanation
How to think about this question
Bigtable stores data in tablets distributed across nodes; garbage collection uses family-level GC policies (e.g., max age or max versions) to automatically delete expired cells during major compactions. Cloud Storage cold storage (e.g., Nearline or Archive) offers lower per-GB costs than Bigtable HDD or SSD storage, and data can be exported via Dataflow or Bigtable backups. The key is that GC policies are applied per column family, so you can keep recent data hot while purging older data without manual intervention.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
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FAQ
Questions learners often ask
What does this PCDE question test?
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use Cloud Storage as a cold storage tier for historical data — The question asks for three strategies, but among the options provided, only two directly reduce storage costs without compromising query performance for the most recent 30 days: Option B (using Cloud Storage as a cold storage tier for historical data) and Option D (setting garbage collection to delete data older than 30 days). Option B offloads old data to cheaper storage while keeping recent data in Bigtable for fast access. Option D automates deletion of stale data, reducing storage footprint without affecting recent queries. The other options are incorrect: increasing nodes (A) raises costs, replication with deletion (C) risks data loss, and reducing nodes (E) would degrade performance for recent data. Thus, the correct answers are B and D, and the question's mention of 'three' is an error in the source material.
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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Last reviewed: Jun 30, 2026
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