PDE Designing data processing systems Practice Question
This PDE practice question tests your understanding of designing data processing systems. 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 uses BigQuery to run reporting queries on a table that is partitioned by date and clustered by customer_id. Queries filtering by customer_id and a date range are performing poorly. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The date range filter is too wide, causing scans of many partitions
Option D is correct because when a table is partitioned by date and clustered by customer_id, queries that filter on both columns can still perform poorly if the date range filter is too wide, causing BigQuery to scan many partitions. Even with clustering, scanning a large number of partitions negates the benefit of clustering, as clustering only reduces the data scanned within each partition. The query optimizer must read all partitions that fall within the date range, and if that range is broad, the scan overhead dominates.
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.
✗
The project lacks sufficient BigQuery slot capacity
Why it's wrong here
Slot capacity would affect all queries similarly; this is a query design issue.
✗
The table is too large for BigQuery
Why it's wrong here
BigQuery handles large tables; performance issues are not due to size alone.
✗
Clustering column order should be date first, then customer_id
Why it's wrong here
Partitioning is on date, clustering on customer_id is fine.
✓
The date range filter is too wide, causing scans of many partitions
Why this is correct
Wide date ranges nullify the benefit of clustering; BigQuery scans many partitions.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume clustering alone guarantees fast queries on any filter combination, without understanding that partition pruning happens first and a wide date range undermines the benefit of clustering.
Trap categories for this question
Similar concept trap
Slot capacity would affect all queries similarly; this is a query design issue.
Detailed technical explanation
How to think about this question
BigQuery uses a columnar storage format (Capacitor) and pruning via partition and cluster metadata. When a query filters on a clustered column, BigQuery uses the clustering metadata to skip blocks that don't match the filter, but this pruning happens only after the partition pruning step. If the date range filter is wide, many partitions are included, and each partition must be scanned for matching customer_id values, reducing the effectiveness of clustering. In practice, a date range covering more than a few days can cause significant performance degradation even with clustering.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Designing data processing systems — This question tests Designing data processing systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The date range filter is too wide, causing scans of many partitions — Option D is correct because when a table is partitioned by date and clustered by customer_id, queries that filter on both columns can still perform poorly if the date range filter is too wide, causing BigQuery to scan many partitions. Even with clustering, scanning a large number of partitions negates the benefit of clustering, as clustering only reduces the data scanned within each partition. The query optimizer must read all partitions that fall within the date range, and if that range is broad, the scan overhead dominates.
What should I do if I get this PDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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