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Linux Foundation PCA Exam - Topic 1 Question 12 Discussion

Which of the following metrics is unsuitable for a Prometheus setup?
D) user_last_login_timestamp_seconds{email='john.doe@example.com'}
A) prometheus_engine_query_log_enabled
B) promhttp_metric_handler_requests_total{code='500'}
C) http_response_total{handler='static/*filepath'}

Linux Foundation PCA Exam - Topic 1 Question 12 Discussion

Actual exam question for Linux Foundation's PCA exam
Question #: 12
Topic #: 1
[All PCA Questions]

Which of the following metrics is unsuitable for a Prometheus setup?

Show Suggested Answer Hide Answer
Suggested Answer: D

The metric user_last_login_timestamp_seconds{email='john.doe@example.com'} is unsuitable for Prometheus because it includes a high-cardinality label (email). Each unique email address would generate a separate time series, potentially numbering in the millions, which severely impacts Prometheus performance and memory usage.

Prometheus is optimized for low- to medium-cardinality metrics that represent system-wide behavior rather than per-user data. High-cardinality metrics cause data explosion, complicating queries and overwhelming the storage engine.

By contrast, the other metrics---prometheus_engine_query_log_enabled, promhttp_metric_handler_requests_total{code='500'}, and http_response_total{handler='static/*filepath'}---adhere to Prometheus best practices. They represent operational or service-level metrics with limited, manageable label value sets.


Extracted and verified from Prometheus documentation -- Metric and Label Naming Best Practices, Cardinality Management, and Anti-Patterns for Metric Design sections.

Contribute your Thoughts:

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Laurene
2 days ago
B is useful for tracking errors.
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Anthony
8 days ago
C seems fine. It's a valid metric.
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Sylvia
13 days ago
I like A. It's a config option, not a metric.
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Brynn
18 days ago
Agreed, D doesn't fit well.
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Barbra
23 days ago
I think D is unsuitable. Too specific.
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Herman
28 days ago
A is the one that stands out as unsuitable.
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Willard
1 month ago
B and C are totally valid metrics, no doubt!
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Elza
1 month ago
Wait, why would D be a problem? Seems fine to me.
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Galen
3 months ago
I think A is the right answer here!
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Tesha
3 months ago
D is definitely not suitable for Prometheus.
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Oren
4 months ago
I’m leaning towards D as well, but I’m not confident. It just seems like it wouldn’t fit the usual metric patterns we discussed.
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Ty
4 months ago
I feel like I've seen a similar question before, and I think it was about the format of the metrics. Could it be A?
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Rebbecca
4 months ago
I'm not entirely sure, but I remember something about metrics needing to be aggregated. Maybe option C is the odd one out?
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Dan
4 months ago
I think option D might be the one that's unsuitable since it seems too specific for Prometheus metrics.
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