Performance Workloads
Turning observed production traffic into a runnable workload, then reading what comes back. Interviewers probe it because an average response time hides almost every problem worth finding.
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- Load Modeling & Measurement5 questions
- Run Shapes13 questions
- Soak & Endurance Runs4 questions
- Spike & Recovery5 questions
- Overload & Degradation4 questions
- Reading Results22 questions
- Percentiles & Tails5 questions
- Errors & Throughput4 questions
- Bottleneck Attribution5 questions
- Run Comparability4 questions
- Pass Criteria4 questions
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questions
page 2 of 2Response times climb across a long steady-load run while per-request resource use stays flat - what do you check?
basics
~20 sCheck whether the climb advances with work done or with elapsed time. Replot it against cumulative completed work, run a low-rate control, probe a path the run never writes to, and restart the process keeping its data.
When extra capacity arrives minutes after a surge, how do you keep a performance run from hiding that delay?
basics
~20 sStart at the size the system would reach under baseline demand, never pre-raised to peak, and timestamp two series: offered demand and capacity actually serving. The interval between them is the exposure window, and what happened inside it is the result.
How do you prove across a demand surge that no unit of work was lost or done twice?
basics
~20 sTag every submitted unit with a unique identifier before demand rises, then reconcile after the observation window: submitted equals completed plus refused plus pending. Separately compare distinct completed identifiers against total completions, because totals alone hide loss and repetition together.
How would you build a workload model from real production traffic and keep it representative over time?
basics
~20 sDerive the transaction mix, arrival shape and data profile from observed traffic rather than opinion, state the reference period, and keep the model a versioned, owned artefact that is re-derived on a schedule instead of ageing into fiction.
When is adopting a new performance reference run legitimate rather than moving the goalposts?
basics
~20 sIt is legitimate when the shift in level has an identified, intentional cause, was reproduced across repeats, and still meets the obligation the team owes. It is a moved goalpost when the reason is that meeting the old figure became inconvenient.
A slowdown reproduces only when requests overlap. How do you design the follow-up performance run that confirms it?
basics
~20 sVary overlap alone. Run the same arrival rate with few busy clients and then with many idle ones: if duration differs, overlap is the cause. Repeat with requests spread across distinct records to locate what is shared.
In a performance run, how much of each reply can you afford to verify in flight?
basics
~20 sOnly checks cheap enough to fit inside the applying side's own budget: a length floor, a required field, a marker. Deep parsing per reply steals the capacity that generates demand, so sample it instead and report what share was verified.
When a 99th percentile is computed from bucketed latency counts, what error do the bucket boundaries introduce?
basics
~20 sThe read-out locates the bucket holding the ranked request, not its time, so the figure carries that bucket's width as uncertainty. Interpolating inside assumes a spread the slow end does not have, and an unbounded top bucket reports nothing at all.
How do you decide whether a long sustained run should hit scheduled and rotational work or avoid it?
basics
~20 sDecide from what the hold must prove. Arrange the run to hit periodic work - scheduled jobs, credential rotation, cache expiry, index maintenance - when that interaction is the risk; otherwise disable it and record that the trend excludes it.
How do you establish that a second, larger request peak after an applied surge was self-inflicted rather than real demand?
basics
~20 sCompare what the load generator offered against what the service received: the offered rate is known and unchanged, so any excess was manufactured inside the system. Repeats of identifiers already submitted, arriving synchronised at a fixed delay, confirm it.
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