Load Profiles

Load profiles control how virtual users are distributed over time during a test. VoltTest supports two approaches: constant load and staged load profiles.

Constant Load

The simplest approach — a fixed number of virtual users for a set duration.

$test = new VoltTest('Constant Load Test');
$test->setVirtualUsers(100);
$test->setDuration('5m');

This runs 100 VUs for 5 minutes. All users start immediately by default.

Ramp-Up

Gradually start virtual users over a period instead of all at once. This avoids a thundering herd hitting your server at second zero.

$test = new VoltTest('Ramped Load Test');
$test->setVirtualUsers(200);
$test->setDuration('10m');
$test->setRampUp('30s');  // Spread user starts over 30 seconds

With ramp-up, VUs start linearly over the specified time:

• At 0s: 0 VUs active
• At 15s: ~100 VUs active
• At 30s: all 200 VUs active
• At 10m: test ends

When to Use Constant Load

• Baseline testing — measure steady-state performance under known load
• Smoke tests — quick sanity check with low VU count
• Endurance tests — sustained load over a long duration to find memory leaks

Staged Load Profiles

Stages let you define a dynamic load profile where VU count changes over time. Each stage linearly ramps from the previous target to a new target over a given duration.

$test = new VoltTest('Staged Test');

$test->stage('1m', 50);    // Ramp up to 50 VUs over 1 minute
$test->stage('5m', 50);    // Hold at 50 VUs for 5 minutes
$test->stage('30s', 200);  // Spike to 200 VUs over 30 seconds
$test->stage('5m', 200);   // Hold at 200 VUs for 5 minutes
$test->stage('1m', 0);     // Ramp down to 0 over 1 minute

Stage Parameters

Parameter	Type	Description
duration	string	How long this stage lasts (<number>[s|m|h])
target	int	Target VU count at the end of this stage

Each stage starts from wherever the previous stage ended. The first stage starts from 0.

Common Patterns

Ramp Up → Hold → Ramp Down

The standard load test pattern. Gradually increase load, sustain it, then wind down.

$test->stage('2m', 100);   // Ramp up
$test->stage('10m', 100);  // Hold
$test->stage('2m', 0);     // Ramp down

Spike Test

Test how your system handles sudden traffic surges.

$test->stage('1m', 50);    // Normal load
$test->stage('5m', 50);    // Hold normal
$test->stage('10s', 500);  // Sudden spike
$test->stage('1m', 500);   // Hold spike
$test->stage('10s', 50);   // Drop back to normal
$test->stage('5m', 50);    // Hold normal
$test->stage('1m', 0);     // Ramp down

Step-Up (Stress Test)

Incrementally increase load to find the breaking point.

$test->stage('1m', 100);   // Step 1
$test->stage('3m', 100);   // Hold
$test->stage('1m', 200);   // Step 2
$test->stage('3m', 200);   // Hold
$test->stage('1m', 400);   // Step 3
$test->stage('3m', 400);   // Hold
$test->stage('1m', 800);   // Step 4
$test->stage('3m', 800);   // Hold
$test->stage('2m', 0);     // Ramp down

Soak Test (Endurance)

Sustained load over a long period to detect memory leaks and degradation.

$test->stage('5m', 100);   // Ramp up
$test->stage('2h', 100);   // Hold for 2 hours
$test->stage('5m', 0);     // Ramp down

When to Use Staged Profiles

• Realistic traffic simulation — real users don't all arrive at once
• Spike testing — simulate flash sales, marketing campaigns, or viral events
• Stress testing — find breaking points by stepping up load incrementally
• Soak testing — long-running tests to find slow memory leaks or connection pool exhaustion

Constant vs Staged

	Constant Load	Staged Profiles
VU count	Fixed for entire test	Changes over time
Setup	setVirtualUsers() + setDuration()	stage() calls
Ramp-up	Optional via setRampUp()	Built into first stage
Complexity	Simple	Flexible
Best for	Baseline, smoke tests	Spike, stress, soak tests

warning

Constant load and staged profiles are mutually exclusive. Using stage() prevents using setVirtualUsers(), setDuration(), and setRampUp() — and vice versa.

Cloud Mode

Both constant and staged profiles work identically in cloud mode:

$test = new VoltTest('Cloud Staged Test');
$test->cloud('vt_your_api_key');

$test->stage('2m', 500);
$test->stage('10m', 500);
$test->stage('2m', 0);

$test->run();

See the Cloud Mode page for details on cloud execution.