Load Testing
Realistic data, realistic mix, and a ramp rather than a step.
5 to work through
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intermediate
A load test passed at 3x expected traffic and production fell over at 1.2x. Name four ways the test could have been unrealistic.
2 min answer -
advanced
A commerce platform load tests successfully at five times peak traffic, then fails during the real peak event. What is typically wrong with the load test?
2 min answer -
advanced
A retail platform's load tests pass comfortably and production fails at the same throughput during a sale. What is different about production?
2 min answer -
advanced
An annual sale will bring 10× normal traffic in a 72-hour window. What preparation should begin months in advance, and what is prepared but hopefully never used?
3 min answer -
advanced
Your load tests pass consistently and production still falls over at peak. What is wrong with the tests?
2 min answer
4 terms in this topic
Breaking-Point Testing
Pushing a load test past the target until the system fails, because the purpose of a load test is to locate the constraint and the failure mode rathe…
conceptCoordinated Omission
The measurement error in which a load generator stops issuing requests while the system under test is stalled, so the slow samples that a real arriva…
practiceLoad Testing in Practice
Verifying behaviour under expected load — where realism of workload and data matters more than the number of virtual users.
practiceWorkload Model
A description of the traffic mix, arrival pattern and data distribution a load test reproduces, which determines whether the test's results mean anything.
Neighbouring topics
Performance & Capacity
General material on performance and capacity engineering.
Latency
Distributions rather than averages, and the floors physics imposes.
Throughput
Work completed per unit time, and why it trades against latency.
Concurrency
Operations in flight, and the limits that are the real capacity ceiling.
Queueing Theory
Why latency explodes as utilisation approaches capacity.
Little's Law
L = λW, and the pool sizes it computes directly.
Bottleneck Analysis
Finding the constraint, and expecting a second one behind it.
Tail Latency
p99 behaviour, amplification across fan-out, and hedged requests.
Stress Testing
Pushing past target to learn what breaks first and how it fails.
Soak Testing
Long runs that surface leaks and slow degradation.
Capacity Modelling
Arithmetic before load tests, and headroom for failure as well as peak.
Horizontal vs Vertical Scaling
Scale out for stateless, scale up first for stateful.
Caching for Performance
Layer choice, hit ratio as a first-class metric, and cold-cache recovery.
Database Performance
Plans, indexes, contention and the pool in front of the database.
Connection Pooling
The most common hidden ceiling, and the metric nobody collects.
Network Performance Tuning
Keep-alive, compression, payload size and round-trip elimination.
Performance Budgets
Targets enforced in CI so regressions fail the build.
Profiling & Optimisation
Measuring before optimising, and optimising the dominant term.
Peak Event Readiness
Freeze, pre-scale, shed order, warm caches and rehearse.