The answer is to remove the `--processing-units` flag and use `--num-nodes=2` when creating the instance. This is correct because Google Cloud Spanner enforces a strict separation between node-based and processing-unit-based configurations: `--num-nodes` provisions dedicated compute and storage capacity for production workloads, while `--processing-units` is designed for smaller, burstable configurations ranging from 100 to 1000 processing units per node equivalent, and the two flags cannot be combined in the same command. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of Spanner instance provisioning and the distinction between fixed node counts and flexible processing units—a common trap is assuming you can specify both flags or that `--processing-units` can scale to full node capacity. Remember the memory tip: "Nodes are for production, processing units are for prototyping—never mix the two flags."
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
Refer to the exhibit.
```
gcloud spanner instances create test-instance \
--config=regional-us-west1 \
--description="Test Instance" \
--nodes=2 \
--processing-units=1000
```
The command output shows an error: "ERROR: (gcloud.spanner.instances.create) INVALID_ARGUMENT: processing_units and nodes cannot be set simultaneously."
What is the correct way to create a Spanner instance with 2 nodes?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the --processing-units flag
In Google Cloud Spanner, the `--num-nodes` flag is the correct way to specify the number of nodes when creating an instance. The `--processing-units` flag is used for smaller, burstable configurations (100–1000 processing units per node equivalent) and cannot be combined with `--num-nodes`. Option C is correct because removing `--processing-units` and using `--num-nodes=2` creates a 2-node instance as required.
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.
✗
Use --num-nodes=2 instead of --nodes
Why it's wrong here
--nodes is correct flag; --num-nodes does not exist.
✗
Set --processing-units=2000 and remove --nodes
Why it's wrong here
That creates an instance with 2000 processing units, not 2 nodes.
✓
Remove the --processing-units flag
Why this is correct
Nodes and processing units are exclusive; remove one.
Related concept
Read the scenario before looking for a memorised answer.
✗
Set --nodes=2 and --processing-units=0
Why it's wrong here
They cannot be set simultaneously regardless of value.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think `--nodes` is a valid flag (it is not) or that `--processing-units` can be combined with `--num-nodes`, when in fact they are mutually exclusive and the correct flag for specifying node count is `--num-nodes`.
Detailed technical explanation
How to think about this question
Google Cloud Spanner instances are provisioned with either `--num-nodes` (for dedicated capacity, each node provides 2 TB of storage and up to 10,000 QPS) or `--processing-units` (for burstable capacity, where 1000 processing units equals 1 node). The two flags cannot be used together; attempting to do so results in a validation error. In production, using `--num-nodes` is preferred for predictable performance and larger storage needs, while `--processing-units` is suitable for development or variable workloads.
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.
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: Remove the --processing-units flag — In Google Cloud Spanner, the `--num-nodes` flag is the correct way to specify the number of nodes when creating an instance. The `--processing-units` flag is used for smaller, burstable configurations (100–1000 processing units per node equivalent) and cannot be combined with `--num-nodes`. Option C is correct because removing `--processing-units` and using `--num-nodes=2` creates a 2-node instance as required.
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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Question Discussion
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