Performance Monitoring

Performance monitoring helps you track the speed and reliability of your application. Sentry captures performance data through transactions and spans, giving you insights into what’s slow and why.

Getting Started

Enable performance monitoring during SDK initialization:

import * as Sentry from '@sentry/browser';

Sentry.init({
  dsn: 'your-dsn',
  
  // Performance Monitoring
  tracesSampleRate: 1.0, // Capture 100% of transactions for performance monitoring
  
  // Session Replay
  replaysSessionSampleRate: 0.1, // Capture 10% of all sessions
  replaysOnErrorSampleRate: 1.0 // Capture 100% of sessions with errors
});

In production, adjust tracesSampleRate to a lower value (e.g., 0.1 for 10%) to reduce data volume and costs.

Sampling

Uniform Sample Rate

Set a fixed sample rate for all transactions:

Sentry.init({
  dsn: 'your-dsn',
  tracesSampleRate: 0.2 // Sample 20% of transactions
});

Dynamic Sampling

Use a function to dynamically sample transactions:

Sentry.init({
  dsn: 'your-dsn',
  tracesSampler: (samplingContext) => {
    // Sample 100% of checkout transactions
    if (samplingContext.name?.includes('checkout')) {
      return 1.0;
    }
    
    // Sample 100% of transactions with errors
    if (samplingContext.parentSampled === true) {
      return 1.0;
    }
    
    // Sample 10% of everything else
    return 0.1;
  }
});

Use tracesSampler for fine-grained control over which transactions to sample based on their context.

Transactions

Transactions represent a single instance of a service being called. Use startSpan to create transactions:

import * as Sentry from '@sentry/browser';

const result = Sentry.startSpan(
  {
    name: 'process_order',
    op: 'function'
  },
  (span) => {
    // Your code here
    const order = processOrder();
    return order;
  }
);

Transaction Operations

Use standard operation names for consistency:

// HTTP requests
Sentry.startSpan({ name: 'GET /api/users', op: 'http.client' }, () => {
  // ...
});

// Database queries
Sentry.startSpan({ name: 'SELECT * FROM users', op: 'db.query' }, () => {
  // ...
});

// Functions
Sentry.startSpan({ name: 'calculateTotal', op: 'function' }, () => {
  // ...
});

// UI rendering
Sentry.startSpan({ name: 'render_component', op: 'ui.react.render' }, () => {
  // ...
});

Async Operations

Transactions work seamlessly with async code:

const userData = await Sentry.startSpan(
  { name: 'fetch_user_data', op: 'http.client' },
  async (span) => {
    const response = await fetch('/api/user');
    const data = await response.json();
    
    // Add custom data to the span
    span.setAttribute('user.id', data.id);
    span.setAttribute('http.status_code', response.status);
    
    return data;
  }
);

Measuring Operations

Basic Timing

Measure how long operations take:

Sentry.startSpan({ name: 'process_payment', op: 'payment' }, (span) => {
  // Validate payment
  validatePaymentInfo();
  
  // Charge card
  const result = chargeCard();
  
  // Send receipt
  sendReceipt();
  
  return result;
});

Nested Operations

Create child spans for detailed timing:

Sentry.startSpan({ name: 'checkout', op: 'function' }, () => {
  // Validate cart
  Sentry.startSpan({ name: 'validate_cart', op: 'function' }, () => {
    validateCart();
  });
  
  // Calculate total
  const total = Sentry.startSpan({ name: 'calculate_total', op: 'function' }, () => {
    return calculateTotal();
  });
  
  // Process payment
  Sentry.startSpan({ name: 'process_payment', op: 'payment' }, () => {
    processPayment(total);
  });
});

Span Attributes

Add custom data to spans:

Sentry.startSpan({ name: 'fetch_products', op: 'http.client' }, (span) => {
  span.setAttribute('category', 'electronics');
  span.setAttribute('limit', 10);
  span.setAttribute('user.premium', true);
  
  const products = fetchProducts({ category: 'electronics', limit: 10 });
  
  span.setAttribute('result.count', products.length);
  
  return products;
});

Span attributes are searchable and can be used for filtering and grouping in the Sentry UI.

Span Status

Set the status of a span to indicate success or failure:

Sentry.startSpan({ name: 'api_request', op: 'http.client' }, (span) => {
  try {
    const response = fetch('/api/data');
    span.setStatus({ code: 1, message: 'ok' }); // OK
    return response;
  } catch (error) {
    span.setStatus({ code: 2, message: 'internal_error' }); // Error
    throw error;
  }
});

Status Codes

0 - UNSET: Default status
1 - OK: Success
2 - ERROR: Error occurred

HTTP Status Codes

Automatically set span status from HTTP responses:

import { setHttpStatus } from '@sentry/browser';

Sentry.startSpan({ name: 'GET /api/users', op: 'http.client' }, async (span) => {
  const response = await fetch('/api/users');
  
  // Set status based on HTTP status code
  setHttpStatus(span, response.status);
  
  return response.json();
});

Custom Measurements

Add custom measurements to spans:

import { setMeasurement } from '@sentry/browser';

Sentry.startSpan({ name: 'render_page', op: 'ui.render' }, (span) => {
  const startMemory = performance.memory?.usedJSHeapSize;
  
  renderPage();
  
  const endMemory = performance.memory?.usedJSHeapSize;
  const memoryUsed = endMemory - startMemory;
  
  // Add custom measurement
  setMeasurement('memory_used', memoryUsed, 'byte');
});

Suppressing Tracing

Temporarily disable tracing for specific operations:

import { suppressTracing } from '@sentry/browser';

suppressTracing(() => {
  // No spans will be created inside this callback
  internalOperation();
  debugLogging();
});

Use suppressTracing sparingly and only when you need to prevent instrumentation of internal operations that would create noise.

Getting Active Span

Access the currently active span:

import { getActiveSpan, spanToJSON } from '@sentry/browser';

Sentry.startSpan({ name: 'parent_operation' }, () => {
  const activeSpan = getActiveSpan();
  
  if (activeSpan) {
    // Get span details
    const spanData = spanToJSON(activeSpan);
    console.log('Trace ID:', spanData.trace_id);
    console.log('Span ID:', spanData.span_id);
    
    // Add attributes to active span
    activeSpan.setAttribute('custom', 'value');
  }
  
  // Child spans will be children of this span
  Sentry.startSpan({ name: 'child_operation' }, () => {
    // ...
  });
});

Integration Examples

React Component

import * as Sentry from '@sentry/react';

function UserProfile({ userId }) {
  const [user, setUser] = React.useState(null);
  
  React.useEffect(() => {
    Sentry.startSpan(
      { name: 'UserProfile.load', op: 'ui.react.component' },
      async () => {
        const userData = await Sentry.startSpan(
          { name: 'fetch_user', op: 'http.client' },
          () => fetch(`/api/users/${userId}`).then(r => r.json())
        );
        
        setUser(userData);
      }
    );
  }, [userId]);
  
  if (!user) return <div>Loading...</div>;
  
  return <div>{user.name}</div>;
}

Express.js Route

import * as Sentry from '@sentry/node';
import express from 'express';

const app = express();

app.get('/api/users/:id', async (req, res) => {
  await Sentry.startSpan(
    {
      name: 'GET /api/users/:id',
      op: 'http.server',
      attributes: {
        'http.method': 'GET',
        'http.route': '/api/users/:id',
        'user.id': req.params.id
      }
    },
    async (span) => {
      // Query database
      const user = await Sentry.startSpan(
        { name: 'SELECT users', op: 'db.query' },
        () => db.users.findById(req.params.id)
      );
      
      span.setAttribute('user.found', !!user);
      
      res.json(user);
    }
  );
});

Best Practices

Use descriptive names: Name transactions and spans clearly to understand what they measure
Set appropriate operations: Use standard operation names for consistency
Add relevant attributes: Include data that helps identify slow operations
Sample wisely: Balance data volume with coverage needs
Measure meaningful operations: Focus on user-facing and critical operations
Keep spans focused: Each span should represent a single logical operation

Performance Impact

Sentry’s performance monitoring is designed to have minimal impact:

Lightweight instrumentation
Efficient sampling
Async processing
No blocking operations

Start with a higher sample rate in development and lower it in production based on your traffic and needs.

Next Steps

Tracing

Learn about distributed tracing

Spans

Deep dive into spans and instrumentation

Distributed Tracing

Track requests across services

Session Replay

Combine performance data with session replay

Error Monitoring

Advanced Features

Performance Monitoring

Getting Started

Sampling

Uniform Sample Rate

Dynamic Sampling

Transactions

Transaction Operations

Async Operations

Measuring Operations

Basic Timing

Nested Operations

Span Attributes

Span Status

Status Codes

HTTP Status Codes

Custom Measurements

Suppressing Tracing

Getting Active Span

Integration Examples

React Component

Express.js Route

Best Practices

Performance Impact

Next Steps

Tracing

Spans

Distributed Tracing

Session Replay

Build docs developers (and LLMs) love

Error Monitoring

Performance Monitoring

Advanced Features

​Getting Started

​Sampling

​Uniform Sample Rate

​Dynamic Sampling

​Transactions

​Transaction Operations

​Async Operations

​Measuring Operations

​Basic Timing

​Nested Operations

​Span Attributes

​Span Status

​Status Codes

​HTTP Status Codes

​Custom Measurements

​Suppressing Tracing

​Getting Active Span

​Integration Examples

​React Component

​Express.js Route

​Best Practices

​Performance Impact

​Next Steps

Tracing

Spans

Distributed Tracing

Session Replay

Build docs developers (and LLMs) love

Getting Started

Sampling

Uniform Sample Rate

Dynamic Sampling

Transactions

Transaction Operations

Async Operations

Measuring Operations

Basic Timing

Nested Operations

Span Attributes

Span Status

Status Codes

HTTP Status Codes

Custom Measurements

Suppressing Tracing

Getting Active Span

Integration Examples

React Component

Express.js Route

Best Practices

Performance Impact

Next Steps