1# Observability Patterns
2 
3## Usage-Based Billing
4 
5```typescript
6env.ANALYTICS.writeDataPoint({
7  blobs: [customerId, request.url, request.method],
8  doubles: [1], // request_count
9  indexes: [customerId]
10});
11```
12 
13```sql
14SELECT blob1 AS customer_id, SUM(_sample_interval * double1) AS total_calls
15FROM api_usage WHERE timestamp >= DATE_TRUNC('month', NOW())
16GROUP BY customer_id
17```
18 
19## Performance Monitoring
20 
21```typescript
22const start = Date.now();
23const response = await fetch(url);
24env.ANALYTICS.writeDataPoint({
25  blobs: [url, response.status.toString()],
26  doubles: [Date.now() - start, response.status]
27});
28```
29 
30```sql
31SELECT blob1 AS url, AVG(double1) AS avg_ms, percentile(double1, 0.95) AS p95_ms
32FROM fetch_metrics WHERE timestamp >= NOW() - INTERVAL '1' HOUR
33GROUP BY url
34```
35 
36## Error Tracking
37 
38```typescript
39env.ANALYTICS.writeDataPoint({
40  blobs: [error.name, request.url, request.method],
41  doubles: [1],
42  indexes: [error.name]
43});
44```
45 
46## Multi-Tenant Tracking
47 
48```typescript
49env.ANALYTICS.writeDataPoint({
50  indexes: [tenantId], // efficient filtering
51  blobs: [tenantId, url.pathname, method, status],
52  doubles: [1, duration, bytesSize]
53});
54```
55 
56## Tail Worker Log Filtering
57 
58```typescript
59export default {
60  async tail(events, env, ctx) {
61    const critical = events.filter(e => 
62      e.exceptions.length > 0 || e.event.wallTime > 1000000
63    );
64    if (critical.length === 0) return;
65    
66    ctx.waitUntil(
67      fetch('https://logging.example.com/ingest', {
68        method: 'POST',
69        headers: { 'Authorization': `Bearer ${env.API_KEY}` },
70        body: JSON.stringify(critical.map(e => ({
71          outcome: e.event.outcome,
72          cpu_ms: e.event.cpuTime / 1000,
73          errors: e.exceptions
74        })))
75      })
76    );
77  }
78};
79```
80 
81## OpenTelemetry Export
82 
83```typescript
84export default {
85  async tail(events, env, ctx) {
86    const otelSpans = events.map(e => ({
87      traceId: generateId(32),
88      spanId: generateId(16),
89      name: e.scriptName || 'worker.request',
90      attributes: [
91        { key: 'worker.outcome', value: { stringValue: e.event.outcome } },
92        { key: 'worker.cpu_time_us', value: { intValue: String(e.event.cpuTime) } }
93      ]
94    }));
95    
96    ctx.waitUntil(
97      fetch('https://api.honeycomb.io/v1/traces', {
98        method: 'POST',
99        headers: { 'X-Honeycomb-Team': env.HONEYCOMB_KEY },
100        body: JSON.stringify({ resourceSpans: [{ scopeSpans: [{ spans: otelSpans }] }] })
101      })
102    );
103  }
104};
105```
106