Counter vs Gauge vs Histogram

Introduction Definitions Step-by-step Processes Best Practices FAQ

Introduction

In the field of monitoring, it's essential to understand the various types of metrics available for collecting and analyzing data. This lesson covers three primary types of metrics: Counter, Gauge, and Histogram. Understanding the differences and use cases for each is crucial for effective monitoring and alerting systems.

Definitions

Counter

A Counter is a cumulative metric that represents a single monotonically increasing value. It can only increase or reset to zero. Use cases include counting requests, errors, or any event that should only accumulate over time.

Gauge

A Gauge is a metric that represents a single numerical value that can arbitrarily go up and down. This is useful for measuring values like temperature, memory usage, or current active sessions.

Histogram

A Histogram samples observations and counts them in configurable buckets. It provides a distribution of values over time, which is useful for understanding the performance of applications, such as request latency.

Step-by-step Processes

How to Implement Each Metric

Implementing a Counter

const { Counter } = require('prom-client');
const requestCounter = new Counter({
    name: 'http_requests_total',
    help: 'Total number of HTTP requests',
    labelNames: ['method']
});

// Increment the counter
requestCounter.inc({ method: 'GET' });

Implementing a Gauge

const { Gauge } = require('prom-client');
const memoryUsageGauge = new Gauge({
    name: 'memory_usage_bytes',
    help: 'Memory usage in bytes'
});

// Set the gauge value
memoryUsageGauge.set(process.memoryUsage().heapUsed);

Implementing a Histogram

const { Histogram } = require('prom-client');
const requestDurationHistogram = new Histogram({
    name: 'http_request_duration_seconds',
    help: 'Duration of HTTP requests in seconds',
    buckets: [0.1, 0.5, 1, 2, 5] // Customize buckets
});

// Observe the duration
requestDurationHistogram.observe(durationInSeconds);

Best Practices

Choose the right metric type based on the data you are collecting.
Always label your metrics for better identification and filtering.
Use counters for events that only increase and gauges for current values.
Utilize histograms for performance metrics where distribution analysis is required.

FAQ

What is the difference between a Counter and a Gauge?

A Counter only increases or resets, while a Gauge can both increase and decrease.

When should I use a Histogram?

Use a Histogram when you want to analyze the distribution of values over time, such as request latencies.

Can a Counter be reset?

Yes, a Counter can be reset to zero, but it should only be done when necessary (e.g., application restart).

Flowchart of Metric Selection Process


            graph TD;
                A[Start] --> B{What to measure?};
                B -- Yes --> C[Event Count];
                B -- No --> D{Is it a value?};
                D -- Yes --> E[Use Gauge];
                D -- No --> F[Use Histogram];
                C --> G[Use Counter];