- A
Enable the PostgreSQL query cache by setting 'query_cache_type' to 'on'.
Why wrong: PostgreSQL does not have a built-in query cache like MySQL. The 'query_cache_type' parameter is not valid in PostgreSQL. The correct approach is to use connection pooling or application-level caching.
- B
Increase the PostgreSQL shared_buffers setting to 4 GB.
Increasing shared_buffers allows PostgreSQL to cache more data in memory, reducing the amount of disk I/O needed. This directly addresses the high disk utilization.
- C
Increase the PostgreSQL max_connections setting to 200.
Why wrong: Increasing max_connections would allow more concurrent database connections, which could increase the disk I/O load, making the problem worse.
- D
Decrease the Apache MaxClients setting to 50.
Why wrong: This would reduce the number of web server workers, but the bottleneck is at the database disk I/O. While it may reduce the number of concurrent database queries, it does not address the root cause or improve performance significantly.
Quick Answer
The correct choice is to increase PostgreSQL’s shared_buffers setting to 4 GB. This directly addresses the disk I/O bottleneck indicated by high disk utilization and await times over 200 ms, because a write-heavy database forces frequent disk writes when the cache is too small. By allocating 25% of the server’s 16 GB RAM to shared_buffers, more data pages remain in memory, reducing the need for physical disk I/O and lowering the load average caused by processes stuck in uninterruptible sleep. On the LFCS exam, this scenario tests your understanding of PostgreSQL memory tuning under I/O pressure—a common real-world sysadmin task. A frequent trap is to increase the buffer pool too high (e.g., over 40% of RAM), which starves the OS and Apache of memory; the safe guideline is 25% for dedicated database servers. Remember the “quarter rule”: for write-heavy workloads, set shared_buffers to roughly one-quarter of total RAM to balance caching with system overhead.
LFCS Operation of Running Systems Practice Question
This LFCS practice question tests your understanding of operation of running 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.
You are a systems administrator for a company that runs a web application on a Linux server with 16 GB of RAM and 4 CPU cores. The application uses Apache with mod_php and PostgreSQL. Recently, the server has been experiencing high load average (above 10) and the website is responding slowly. The 'top' command shows that many 'httpd' processes are in 'D' (uninterruptible sleep) state. The 'iostat -x 1' output shows high disk utilization (over 90%) and high average wait times (await > 200 ms) on the disk where PostgreSQL data is stored. The database is write-heavy, and you suspect that disk I/O is the bottleneck. Which of the following actions is most likely to improve the performance?
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 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
Increase the PostgreSQL shared_buffers setting to 4 GB.
The high disk utilization (over 90%) and high await times (>200 ms) on the PostgreSQL data disk indicate that the database is I/O-bound. Increasing PostgreSQL's shared_buffers to 4 GB (25% of 16 GB RAM) allows more data to be cached in memory, reducing the frequency of disk writes and reads for write-heavy workloads. This directly alleviates the disk I/O bottleneck, lowering the load average and the number of httpd processes in 'D' state.
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.
- ✗
Enable the PostgreSQL query cache by setting 'query_cache_type' to 'on'.
Why it's wrong here
PostgreSQL does not have a built-in query cache like MySQL. The 'query_cache_type' parameter is not valid in PostgreSQL. The correct approach is to use connection pooling or application-level caching.
- ✓
Increase the PostgreSQL shared_buffers setting to 4 GB.
Why this is correct
Increasing shared_buffers allows PostgreSQL to cache more data in memory, reducing the amount of disk I/O needed. This directly addresses the high disk utilization.
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.
- ✗
Increase the PostgreSQL max_connections setting to 200.
Why it's wrong here
Increasing max_connections would allow more concurrent database connections, which could increase the disk I/O load, making the problem worse.
- ✗
Decrease the Apache MaxClients setting to 50.
Why it's wrong here
This would reduce the number of web server workers, but the bottleneck is at the database disk I/O. While it may reduce the number of concurrent database queries, it does not address the root cause or improve performance significantly.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse PostgreSQL's shared_buffers with MySQL's query cache or think that reducing Apache connections will fix an I/O bottleneck, when the real solution is to increase database memory caching to reduce disk pressure.
Detailed technical explanation
How to think about this question
PostgreSQL's shared_buffers is the primary memory cache for database pages; setting it too high (e.g., >40% of RAM) can cause double caching with the OS page cache, while setting it too low forces more disk reads/writes. In a write-heavy workload, increasing shared_buffers reduces the need to flush dirty pages to disk frequently, lowering I/O wait. The 'D' state in top indicates processes waiting for I/O completion, which is a classic sign of a saturated storage subsystem.
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 practitioner preparing for the LFCS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
- →
Operation of Running Systems — study guide chapter
Learn the concepts, then practise the questions
- →
Operation of Running Systems practice questions
Targeted practice on this topic area only
- →
All LFCS questions
513 questions across all exam domains
- →
Linux Foundation Certified System Administrator LFCS study guide
Full concept coverage aligned to exam objectives
- →
LFCS practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related LFCS practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
User and Group Management practice questions
Practise LFCS questions linked to User and Group Management.
Operation of Running Systems practice questions
Practise LFCS questions linked to Operation of Running Systems.
Essential Commands practice questions
Practise LFCS questions linked to Essential Commands.
Networking practice questions
Practise LFCS questions linked to Networking.
Service Configuration practice questions
Practise LFCS questions linked to Service Configuration.
Storage Management practice questions
Practise LFCS questions linked to Storage Management.
LFCS fundamentals practice questions
Practise LFCS questions linked to LFCS fundamentals.
LFCS scenario practice questions
Practise LFCS questions linked to LFCS scenario.
LFCS troubleshooting practice questions
Practise LFCS questions linked to LFCS troubleshooting.
Practice this exam
Start a free LFCS practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this LFCS question test?
Operation of Running Systems — This question tests Operation of Running Systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the PostgreSQL shared_buffers setting to 4 GB. — The high disk utilization (over 90%) and high await times (>200 ms) on the PostgreSQL data disk indicate that the database is I/O-bound. Increasing PostgreSQL's shared_buffers to 4 GB (25% of 16 GB RAM) allows more data to be cached in memory, reducing the frequency of disk writes and reads for write-heavy workloads. This directly alleviates the disk I/O bottleneck, lowering the load average and the number of httpd processes in 'D' state.
What should I do if I get this LFCS 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 11, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.