Session Analytics

Overview

Loom’s session analytics system tracks user engagement periods to enable release health metrics like crash-free rate and adoption tracking. Uses hybrid storage: individual sessions for recent data (30 days) and hourly aggregates for historical dashboards.

Sessions integrate with crash tracking for crashed session detection and analytics for person identity.

Key Features

Session tracking for web, Node.js, and Rust applications
Release health metrics: crash-free rate, adoption percentage
Hybrid storage: individual sessions (30 days) + hourly aggregates (forever)
Sampling support for high-volume applications
Real-time updates via SSE for release health changes

Core Concepts

Session

A single user engagement period:

pub struct Session {
    pub id: SessionId,
    pub person_id: Option<PersonId>,
    pub distinct_id: String,
    pub status: SessionStatus,
    pub release: Option<String>,
    pub environment: String,
    pub error_count: u32,           // Handled errors
    pub crash_count: u32,           // Unhandled errors
    pub crashed: bool,              // crash_count > 0
    pub started_at: DateTime<Utc>,
    pub ended_at: Option<DateTime<Utc>>,
    pub duration_ms: Option<u64>,
    pub platform: Platform,
    pub sampled: bool,
    pub sample_rate: f64,
}

Session statuses:

Status	Description
`Active`	Session ongoing
`Exited`	Ended normally (user closed tab, app backgrounded)
`Crashed`	Had at least one unhandled error
`Abnormal`	Ended unexpectedly (no end signal)
`Errored`	Had handled errors but completed normally

Platform Types

pub enum Platform {
    JavaScript,  // Browser
    Node,        // Node.js
    Rust,
    Python,
}

Release Health

Computed metrics for a release:

pub struct ReleaseHealth {
    pub release: String,
    pub environment: String,
    pub total_sessions: u64,
    pub crashed_sessions: u64,
    pub total_users: u64,
    pub crashed_users: u64,
    pub crash_free_session_rate: f64,   // Percentage
    pub crash_free_user_rate: f64,      // Percentage
    pub adoption_rate: f64,             // Percentage
    pub adoption_stage: AdoptionStage,
}

Adoption stages:

Stage	Adoption Rate
`New`	< 5%
`Growing`	5-50%
`Adopted`	50-95%
`Replaced`	< 5% (was higher before)

Automatic Tracking

Sessions are automatically tracked by the crash SDK:

Rust
TypeScript (Browser)
Node.js

use loom_crash::CrashClient;

// Sessions enabled by default
let crash = CrashClient::builder()
    .api_key("loom_crash_xxx")
    .release(env!("CARGO_PKG_VERSION"))
    .with_session_tracking(true)   // Default: true
    .session_sample_rate(1.0)      // Default: 1.0 (100%)
    .build()?;

// Session starts automatically on build()

// Errors update session
crash.capture_error(&error);  // Increments error_count
// Unhandled errors mark as crashed

// Session ends on shutdown
crash.shutdown().await?;

import { CrashClient } from '@loom/crash';

const crash = new CrashClient({
  apiKey: 'loom_crash_xxx',
  release: '1.2.3',
  
  // Session options
  autoSessionTracking: true,      // Default: true
  sessionSampleRate: 1.0,         // Default: 1.0
});

// Session starts automatically
// Session ends on page unload or manual call
crash.endSession();

import { CrashClient } from '@loom/crash';

const crash = new CrashClient({
  apiKey: 'loom_crash_xxx',
  release: '1.2.3',
  autoSessionTracking: true,
});

// Session starts on init
// Session ends on process exit or manual call
process.on('SIGTERM', async () => {
  await crash.endSession();
  process.exit(0);
});

Session Lifecycle

Web (Browser)

Page Load

Session starts when SDK initializes

User Activity

Session remains active while user interacts

Tab/Window Close

Session ends via beforeunload or pagehide event

Visibility Timeout

If page hidden for 30+ minutes, session ends and new one starts when visible again

Node.js / Rust

Process Start

Session starts when crash client initializes

Process Exit

Session ends normally on clean shutdown

Uncaught Exception

Session marked as Crashed on unhandled error

Sampling

For high-traffic applications, reduce storage with sampling:

const crash = new CrashClient({
  apiKey: 'loom_crash_xxx',
  release: '1.2.3',
  
  // Sample 10% of normal sessions
  sessionSampleRate: 0.1,
  
  // Always store crashed sessions (default: true)
  alwaysStoreCrashed: true,
});

Crashed sessions are always stored regardless of sample rate. Only successful sessions are sampled.

Sampling Rules

Base sample rate (e.g., 0.1 = 10%)
Always store crashed (recommended: true)
Metrics are automatically adjusted for sample rate

Example calculation:

Sampled sessions: 1,000
Crashed sessions: 50 (always stored)
Sample rate: 0.1 (10%)

Adjusted total = 50 + ((1000 - 50) / 0.1) = 9,550
Crash-free rate = (9550 - 50) / 9550 = 99.48%

Release Health Metrics

Crash-Free Session Rate

Percentage of sessions without unhandled errors:

crash_free_session_rate = 
  (total_sessions - crashed_sessions) / total_sessions × 100

Example:

Total sessions: 10,000
Crashed sessions: 50
Crash-free rate: 99.5%

Crash-Free User Rate

Percentage of users who didn’t experience crashes:

crash_free_user_rate = 
  (total_users - crashed_users) / total_users × 100

Example:

Total users: 1,000
Users with crashes: 25
Crash-free user rate: 97.5%

User rate is typically lower than session rate because one user can have multiple sessions.

Adoption Rate

Percentage of traffic on this release:

adoption_rate = 
  release_sessions / all_sessions × 100

Example:

Release 1.2.3 sessions: 7,500
All sessions: 10,000
Adoption rate: 75% (Adopted stage)

API Endpoints

Session Ingestion (SDK)

POST /api/sessions/start

endpoint

Start a sessionRequest:

{
  "session_id": "ses_xxx",
  "distinct_id": "user_123",
  "release": "1.2.3",
  "environment": "production",
  "platform": "javascript",
  "started_at": "2026-01-18T12:00:00Z",
  "sample_rate": 1.0
}

POST /api/sessions/end

endpoint

End a sessionRequest:

{
  "session_id": "ses_xxx",
  "status": "exited",
  "error_count": 0,
  "crash_count": 0,
  "ended_at": "2026-01-18T12:30:00Z",
  "duration_ms": 1800000
}

Release Health (User Auth)

GET /api/projects/:id/releases

endpoint

List releases with health metricsQuery Parameters:

environment - Filter by environment
start_date - Start of time range
end_date - End of time range

Response:

{
  "releases": [
    {
      "release": "1.2.3",
      "environment": "production",
      "crash_free_session_rate": 99.5,
      "crash_free_user_rate": 97.8,
      "adoption_rate": 75.2,
      "adoption_stage": "adopted",
      "total_sessions": 10000,
      "crashed_sessions": 50,
      "total_users": 1500
    }
  ]
}

GET /api/projects/:id/releases/:version

endpoint

Get detailed health for specific releaseResponse:

{
  "release": "1.2.3",
  "environment": "production",
  "crash_free_session_rate": 99.5,
  "crash_free_user_rate": 97.8,
  "adoption_rate": 75.2,
  "adoption_stage": "adopted",
  "total_sessions": 10000,
  "crashed_sessions": 50,
  "total_users": 1500,
  "crashed_users": 33,
  "first_seen": "2026-01-15T00:00:00Z",
  "last_seen": "2026-01-18T12:00:00Z",
  "crash_free_rate_trend": 0.2
}

GET /api/projects/:id/health/trend

endpoint

Get health trend over timeQuery Parameters:

interval - hour, day, week
start_date - Start timestamp
end_date - End timestamp

Response:

{
  "trend": [
    {
      "timestamp": "2026-01-15T00:00:00Z",
      "crash_free_session_rate": 99.2,
      "crash_free_user_rate": 97.5,
      "total_sessions": 2000
    },
    {
      "timestamp": "2026-01-16T00:00:00Z",
      "crash_free_session_rate": 99.5,
      "crash_free_user_rate": 97.8,
      "total_sessions": 2100
    }
  ]
}

Session Queries

GET /api/projects/:id/sessions

endpoint

List recent sessionsQuery Parameters:

release - Filter by release
status - Filter by status (active, exited, crashed)
limit - Max results (default: 100)

GET /api/projects/:id/sessions/:sessionId

endpoint

Get session detailResponse:

{
  "session": {
    "id": "ses_xxx",
    "person_id": "per_yyy",
    "status": "exited",
    "release": "1.2.3",
    "environment": "production",
    "error_count": 2,
    "crash_count": 0,
    "duration_ms": 1800000,
    "platform": "javascript",
    "started_at": "2026-01-18T12:00:00Z",
    "ended_at": "2026-01-18T12:30:00Z"
  }
}

Real-time Updates (SSE)

Subscribe to release health changes:

const eventSource = new EventSource(
  'https://loom.example.com/api/projects/proj-123/sessions/stream',
  { headers: { Authorization: 'Bearer <token>' } }
);

eventSource.addEventListener('release.health_changed', (event) => {
  const data = JSON.parse(event.data);
  console.log(`Release ${data.release}: ${data.crash_free_session_rate}% crash-free`);
  updateDashboard(data);
});

Events:

session.started - New session started
session.ended - Session ended
session.crashed - Session marked as crashed
release.health_changed - Release health metrics updated

Aggregation & Retention

Storage Strategy

Individual Sessions

Retention: 30 daysPurpose: Debugging, detailed analysisFull session data with all context

Hourly Aggregates

Retention: ForeverPurpose: Long-term dashboards, trendsRolled-up counts and statistics

Hourly Aggregation

Every hour, individual sessions are aggregated:

SELECT
  release,
  environment,
  COUNT(*) as total_sessions,
  SUM(CASE WHEN status = 'crashed' THEN 1 ELSE 0 END) as crashed_sessions,
  COUNT(DISTINCT person_id) as unique_users,
  COUNT(DISTINCT CASE WHEN crashed = 1 THEN person_id END) as crashed_users,
  AVG(duration_ms) as avg_duration_ms
FROM sessions
WHERE started_at >= ? AND started_at < ?
GROUP BY release, environment

After 30 days, individual sessions are deleted but aggregates remain.

Metric Definitions

Metric	Formula	Description
Crash-free session rate	`(total - crashed) / total × 100`	% sessions without unhandled errors
Crash-free user rate	`(users - crashed_users) / users × 100`	% users without crashes
Adoption rate	`release_sessions / all_sessions × 100`	% traffic on this release
Error rate	`errored / total × 100`	% sessions with handled errors

Best Practices

Set Release Version

Always set release to track health per versionUse semantic versioning or commit SHA

Use Sampling

For high-traffic apps, sample normal sessionsCrashed sessions are always stored

Monitor Trends

Track crash-free rate trends over timeAlert on significant drops

Environment Separation

Separate production/staging environmentsMonitor both independently

Crash Tracking

Investigate crashed sessions

Analytics

Link sessions to person profiles

Get Started

Core Features

Architecture

Integrations

Observability

Deployment

​Overview

​Key Features

​Core Concepts

​Session

​Platform Types

​Release Health

​Automatic Tracking

​Session Lifecycle

​Web (Browser)

​Node.js / Rust

​Sampling

​Sampling Rules

​Release Health Metrics

​Crash-Free Session Rate

​Crash-Free User Rate

​Adoption Rate

​API Endpoints

​Session Ingestion (SDK)

​Release Health (User Auth)

​Session Queries

​Real-time Updates (SSE)

​Aggregation & Retention

​Storage Strategy

Individual Sessions

Hourly Aggregates

​Hourly Aggregation

​Metric Definitions

​Best Practices

Set Release Version

Use Sampling

Monitor Trends

Environment Separation

​See Also

Crash Tracking

Analytics

Build docs developers (and LLMs) love

Overview

Key Features

Core Concepts

Session

Platform Types

Release Health

Automatic Tracking

Session Lifecycle

Web (Browser)

Node.js / Rust

Sampling

Sampling Rules

Release Health Metrics

Crash-Free Session Rate

Crash-Free User Rate

Adoption Rate

API Endpoints

Session Ingestion (SDK)

Release Health (User Auth)

Session Queries

Real-time Updates (SSE)

Aggregation & Retention

Storage Strategy

Hourly Aggregation

Metric Definitions

Best Practices

See Also