The answer is inefficient database queries causing high CPU usage. When strace reveals frequent epoll_wait calls, the process is spending time waiting for I/O events, while numerous futex calls indicate heavy contention over mutexes or synchronization primitives. Together, these system calls point to a database process that is blocking on disk I/O or lock contention, forcing the kernel to schedule other tasks and artificially inflating the system load. On the CompTIA Linux+ XK0-005 exam, this scenario tests your ability to correlate strace output with real-world performance bottlenecks; a common trap is assuming epoll_wait always means idle waiting, when in fact it can mask high CPU usage from inefficient queries that thrash the buffer pool. A useful memory tip is “epoll waits, futex fights” — if you see both, suspect a database struggling with I/O or locking, not a truly idle process.
XK0-005 Troubleshooting Practice Question
This XK0-005 practice question tests your understanding of troubleshooting. 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 database server running on Linux is experiencing high load. The administrator runs 'strace -p <pid>' and sees many 'epoll_wait' and 'futex' calls. Which THREE of the following are possible causes of the high load? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disk I/O contention causing processes to wait.
Option A is correct because 'epoll_wait' indicates the process is waiting for I/O events, and 'futex' calls are used for synchronization. Disk I/O contention can cause the database process to block on these system calls, leading to high load as the kernel schedules other tasks while waiting for I/O to complete.
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.
✓
Disk I/O contention causing processes to wait.
Why this is correct
Waiting on I/O increases load average as processes are in uninterruptible sleep.
Related concept
Read the scenario before looking for a memorised answer.
✓
A large number of concurrent connections.
Why this is correct
Many connections lead to context switching and contention.
Related concept
Read the scenario before looking for a memorised answer.
✗
CPU frequency scaling is set to powersave.
Why it's wrong here
Powersave would reduce CPU speed, potentially lowering load but causing performance issues.
✗
A memory leak in the database process.
Why it's wrong here
Memory leak would cause swapping, not necessarily the observed syscalls.
✓
Inefficient database queries causing high CPU usage.
Why this is correct
Inefficient queries increase CPU usage, visible via strace.
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 may incorrectly associate 'futex' calls solely with memory issues or CPU scaling, rather than recognizing them as indicators of thread contention and I/O waiting under high concurrency.
Detailed technical explanation
How to think about this question
The 'epoll_wait' system call is used for efficient I/O event monitoring in Linux, often employed by database servers to handle many file descriptors. 'futex' (fast userspace mutex) calls are used for thread synchronization; a high frequency of these calls can indicate contention for locks, which can occur under heavy concurrent load or inefficient query execution. In a real-world scenario, a database with many concurrent connections may cause both epoll_wait (waiting for network I/O) and futex (contention for internal locks) to spike, leading to high system load.
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 XK0-005 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Disk I/O contention causing processes to wait. — Option A is correct because 'epoll_wait' indicates the process is waiting for I/O events, and 'futex' calls are used for synchronization. Disk I/O contention can cause the database process to block on these system calls, leading to high load as the kernel schedules other tasks while waiting for I/O to complete.
What should I do if I get this XK0-005 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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