Analytics Engine Gotchas

Critical Issues

Sampling at High Volumes

Problem: Queries return fewer points than written at >1M writes/min.

Solution:

// Pre-aggregate before writing
let buffer = { count: 0, total: 0 };
buffer.count++; buffer.total += value;

// Write once per second instead of per request
if (Date.now() % 1000 === 0) {
  env.ANALYTICS.writeDataPoint({ doubles: [buffer.count, buffer.total] });
}

Detection: npx wrangler tail → look for "sampling enabled"

writeDataPoint Returns void

// ❌ Pointless await
await env.ANALYTICS.writeDataPoint({...});

// ✅ Fire-and-forget
env.ANALYTICS.writeDataPoint({...});

Writes can fail silently. Check tail logs.

Index vs Blob

// ✅ Correct
{ blobs: [method, path, status], indexes: [userId] }

Can't Query from Workers

Query API requires HTTP auth. Use external service or cache in KV/D1.

No Custom Timestamps

Auto-generated at write time. Store original in blob if needed.

Common Errors

Limits

Best Practices

✅ Pre-aggregate at high volumes
✅ Use index for high-cardinality (millions)
✅ Always include time filter in queries
✅ Design schema before coding

❌ Don't await writeDataPoint
❌ Don't use index for low-cardinality
❌ Don't query without time range
❌ Don't assume all writes succeed