---
title: Context, Cardinality, and Dimensionality
impact: CRITICAL
tags: logging, context, cardinality, dimensionality
---
## Context, Cardinality, and Dimensionality
**Impact: CRITICAL**
Wide events must be context-rich with high cardinality and high dimensionality. This enables you to answer questions you haven't anticipated yet - the "unknown unknowns" that traditional logging misses.
### High Cardinality
High cardinality means a field can have millions or billions of unique values. User IDs, request IDs, and transaction IDs are high cardinality fields. Your logging must support querying against any specific value of these fields. Without high cardinality support, you cannot debug issues for specific users.
### High Dimensionality
High dimensionality means your events have many fields (20-100+). More dimensions mean more questions you can answer without redeploying code.
```typescript
const wideEvent = {
// Timing
timestamp: '2024-09-08T06:14:05.680Z',
duration_ms: 268,
// Request context
method: 'POST',
path: '/checkout',
requestId: 'req_abc123',
// Infrastructure
service: 'checkout-service',
version: '2.4.1',
region: 'us-east-1',
commit_hash: '690de31f',
// User context (HIGH CARDINALITY - millions of unique values)
user: {
id: 'user_456',
subscription: 'premium',
account_age_days: 847,
lifetime_value_cents: 284700,
},
// Business context
cart: {
id: 'cart_xyz',
item_count: 3,
total_cents: 15999,
coupon_applied: 'SAVE20',
},
// Payment details
payment: {
method: 'card',
provider: 'stripe',
latency_ms: 189,
},
// Feature flags - crucial for debugging rollouts
feature_flags: {
new_checkout_flow: true,
},
// Outcome
status_code: 200,
outcome: 'success',
};
```
### Always Include Business Context
Include business-specific context, not just technical details. User subscription tier, cart value, feature flags, account age - this context helps prioritize issues and understand business impact.
```typescript
const wideEvent = {
requestId: 'req_123',
method: 'POST',
path: '/checkout',
status_code: 500,
// Business context that changes response priority
user: {
id: 'user_456',
subscription: 'enterprise', // High-value customer
account_age_days: 1247, // Long-term customer
lifetime_value_cents: 4850000, // $48,500 LTV
},
cart: {
total_cents: 249900, // $2,499 order
contains_annual_plan: true, // Recurring revenue at stake
},
feature_flags: {
new_payment_flow: true, // Was new code involved?
},
error: {
type: 'PaymentError',
code: 'card_declined',
},
};
// Now you KNOW this is critical: Enterprise customer, $48.5k LTV,
// trying to make a $2.5k purchase, and new_payment_flow is enabled
```
Business context transforms debugging from "something broke" to "this $48,500 customer can't complete a $2,499 order."
### Always Include Environment Characteristics
Include environment and deployment information in every wide event. This context is essential for correlating issues with deployments, identifying region-specific problems, and understanding the runtime environment.
**Environment fields to include:**
```typescript
const wideEvent = {
// ... request and business context
// Environment characteristics
env: {
// Deployment info
commit_hash: process.env.COMMIT_SHA || process.env.GIT_COMMIT,
version: process.env.SERVICE_VERSION || process.env.npm_package_version,
deployment_id: process.env.DEPLOYMENT_ID,
deploy_time: process.env.DEPLOY_TIMESTAMP,
// Infrastructure
service: process.env.SERVICE_NAME,
region: process.env.AWS_REGION || process.env.REGION,
availability_zone: process.env.AWS_AVAILABILITY_ZONE,
instance_id: process.env.INSTANCE_ID || process.env.HOSTNAME,
container_id: process.env.CONTAINER_ID,
// Runtime
node_version: process.version,
runtime: process.env.AWS_EXECUTION_ENV || 'node',
memory_limit_mb: process.env.AWS_LAMBDA_FUNCTION_MEMORY_SIZE,
// Environment type
environment: process.env.NODE_ENV || process.env.ENVIRONMENT,
stage: process.env.STAGE,
},
};
```
**Why environment context matters:**
- **commit_hash**: Instantly identify which code version caused an issue
- **deployment_id**: Correlate errors with specific deployments
- **region/availability_zone**: Identify region-specific failures
- **instance_id**: Debug issues affecting specific instances
- **version**: Track issues across service versions
- **environment**: Distinguish production from staging issues
This environment context should be added once at service startup and automatically included in every wide event via middleware.
