In monitoring systems like Grafana (using Prometheus as a data source), the rate() function is essential for visualizing counter metrics. A "Counter" is a cumulative metric that represents a single monotonically increasing counter whose value can only increase or be reset to zero on restart.
Common examples of counters include:
Total HTTP requests served
Total tasks completed
Total errors occurred
Total bytes sent
However, visualizing the total raw count (e.g., "1,050,400 requests") is rarely useful for identifying traffic spikes. Instead, engineers need to see the "speed" of the counter, which is requests per second.
The Logic Behind Rate()
This calculator simulates how the rate() function processes data points. It takes the value at the end of a time window, subtracts the value at the start, and divides by the duration in seconds.
Previous Metric Value: The counter value at the start of your query range (e.g., [5m] ago).
Current Metric Value: The counter value at the specific timestamp you are querying.
Time Interval: The range vector selector. In PromQL, this is the value inside the brackets, such as rate(http_requests_total[5m]) where 5m is the interval.
Rate vs. Irate
While rate() calculates the per-second average over the entire specified time range (good for smooth graphs and alerting), irate() calculates the rate based on the last two data points only. This calculator uses the standard rate() logic, averaging the increase over the full duration provided.
Handling Counter Resets
In a real production environment, counters reset to zero when an application restarts. Prometheus handles this automatically by detecting if the value decreased and assuming a reset occurred, effectively adding the previous total to the new count. This calculator simplifies the logic to a standard delta calculation; if your current value is lower than your previous value, it indicates a reset or data anomaly.
function calculateGrafanaRate() {
// Get Input Values
var startVal = parseFloat(document.getElementById('startValue').value);
var endVal = parseFloat(document.getElementById('endValue').value);
var duration = parseFloat(document.getElementById('duration').value);
var timeMultiplier = parseFloat(document.getElementById('timeUnit').value);
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('results');
// Reset display
errorDiv.style.display = 'none';
resultsDiv.style.display = 'none';
// Validation
if (isNaN(startVal) || isNaN(endVal) || isNaN(duration)) {
errorDiv.innerHTML = "Please enter valid numeric values for all fields.";
errorDiv.style.display = 'block';
return;
}
if (duration <= 0) {
errorDiv.innerHTML = "Duration must be greater than zero.";
errorDiv.style.display = 'block';
return;
}
// Calculation Logic
// 1. Calculate the change in the counter (Delta)
var delta = endVal – startVal;
// 2. Convert duration to seconds (Rate is always per-second in PromQL)
var timeInSeconds = duration * timeMultiplier;
// 3. Handle negative delta (Simple warning logic for this calculator)
if (delta < 0) {
errorDiv.innerHTML = "Warning: Current value is less than Previous value. This usually indicates a counter reset.";
errorDiv.style.display = 'block';
// In strict math, we calculate rate based on raw diff, but usually we'd absolute or adjust.
// For this specific tool, we will show negative rate to indicate drop, but warn user.
}
// 4. Calculate Rate (per second)
var ratePerSecond = delta / timeInSeconds;
// 5. Calculate Rate (per minute) – useful for "RPM" visualization
var ratePerMinute = ratePerSecond * 60;
// Display Results
document.getElementById('rateResult').innerHTML = ratePerSecond.toFixed(4) + " /s";
document.getElementById('deltaResult').innerHTML = delta.toLocaleString(); // Shows total increase
document.getElementById('secondsResult').innerHTML = timeInSeconds + " seconds";
document.getElementById('rpmResult').innerHTML = ratePerMinute.toFixed(2) + " /m";
// Show result container
resultsDiv.style.display = 'block';
}