C100DBA Server Administration Practice Question
During a peak load period, the 'page faults' metric in mongostat increases significantly. What is the most likely administrative cause related to server resources?
⚠ Common exam trap
Candidates often confuse 'page faults' in mongostat with OS-level memory paging to disk swap space, forgetting that in MongoDB it specifically refers to documents read from disk files because they are missing from resident RAM.
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
✓
The working set exceeds the available physical RAM.
Page faults occur when the mongod process attempts to access data that is not currently in the physical RAM (resident memory). While some page faults are normal, a sudden spike usually indicates that the 'working set' (the data and indexes accessed most frequently) has grown larger than the available RAM, forcing frequent disk reads.
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 working set exceeds the available physical RAM.
Why this is correct
When the data and indexes required for active operations no longer fit in the WiredTiger cache and OS filesystem cache, MongoDB must fetch data from disk. This process is much slower than memory access and is recorded as a page fault, leading to increased latency and decreased throughput.
- ✗
The number of concurrent connections has reached the 'maxConns' limit.
Why it's wrong here
Reaching the 'maxConns' limit will cause the server to reject new connection attempts, resulting in 'connection refused' errors for clients. While this is a serious resource issue, it does not directly cause page faults, as page faults are related to data access patterns rather than the connection pool size.
- ✗
The CPU is throttled due to excessive BSON serialization.
Why it's wrong here
CPU throttling impacts the processing speed of computations, such as aggregations or document parsing. While it slows down the database, it does not trigger page faults. Page faults are strictly a memory management event where the requested memory page is missing from the RAM and must be retrieved from storage.
- ✗
The journaling frequency is set too high for the disk subsystem.
Why it's wrong here
High journaling frequency increases disk write pressure and can lead to I/O wait, but it does not cause the OS to fault pages into memory. Page faults are a result of read operations (or write-misses) where the data isn't in memory, whereas journaling is a background write process for durability.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DBA practice question is part of Courseiva's free MongoDB certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the C100DBA exam.