1# Gotchas
2 
3See [README.md](./README.md), [configuration.md](./configuration.md), [api.md](./api.md), [patterns.md](./patterns.md).
4 
5## Common Errors
6 
7### "Too many open connections" / "Connection limit exceeded"
8 
9**Cause:** Workers have a hard limit of **6 concurrent connections per invocation**  
10**Solution:** Set `max: 5` in driver config, reuse connections, ensure proper cleanup with `client.end()` or `ctx.waitUntil(conn.end())`
11 
12### "Failed to acquire a connection (Pool exhausted)"
13 
14**Cause:** All connections in pool are in use, often due to long-running transactions  
15**Solution:** Reduce transaction duration, avoid queries >60s, don't hold connections during external calls, or upgrade to paid plan for more connections
16 
17### "connection_refused"
18 
19**Cause:** Database refusing connections due to firewall, connection limits, or service down  
20**Solution:** Check firewall allows Cloudflare IPs, verify DB listening on port, confirm service running, and validate credentials
21 
22### "Query timeout (deadline exceeded)"
23 
24**Cause:** Query execution exceeding 60s timeout limit  
25**Solution:** Optimize with indexes, reduce dataset with LIMIT, break into smaller queries, or use async processing
26 
27### "password authentication failed"
28 
29**Cause:** Invalid credentials in Hyperdrive configuration  
30**Solution:** Check username and password in Hyperdrive config match database credentials
31 
32### "SSL/TLS connection error"
33 
34**Cause:** SSL/TLS configuration mismatch between Hyperdrive and database  
35**Solution:** Add `sslmode=require` (Postgres) or `sslMode=REQUIRED` (MySQL), upload CA cert if self-signed, verify DB has SSL enabled, and check cert expiry
36 
37### "Queries not being cached"
38 
39**Cause:** Query is mutating (INSERT/UPDATE/DELETE), contains volatile functions (NOW(), RANDOM()), or caching disabled  
40**Solution:** Verify query is non-mutating SELECT, avoid volatile functions, confirm caching enabled, use `wrangler dev --remote` to test, and set `prepare=true` for postgres.js
41 
42### "Slow multi-query Workers despite Hyperdrive"
43 
44**Cause:** Worker executing at edge, each query round-trips to DB region  
45**Solution:** Enable Smart Placement (`"placement": {"mode": "smart"}` in wrangler.jsonc) to execute Worker near DB. See [patterns.md](./patterns.md) Multi-Query pattern.
46 
47### "Local database connection failed"
48 
49**Cause:** `localConnectionString` incorrect or database not running  
50**Solution:** Verify `localConnectionString` correct, check DB running, confirm env var name matches binding, and test with psql/mysql client
51 
52### "Environment variable not working"
53 
54**Cause:** Environment variable format incorrect or not exported  
55**Solution:** Use format `CLOUDFLARE_HYPERDRIVE_LOCAL_CONNECTION_STRING_<BINDING>`, ensure binding matches wrangler.jsonc, export variable in shell, and restart wrangler dev
56 
57## Limits
58 
59| Limit | Free | Paid | Notes |
60|-------|------|------|-------|
61| Max configs | 10 | 25 | Hyperdrive configurations per account |
62| Worker connections | 6 | 6 | Max concurrent connections per Worker invocation |
63| Username/DB name | 63 bytes | 63 bytes | Maximum length |
64| Connection timeout | 15s | 15s | Time to establish connection |
65| Idle timeout | 10 min | 10 min | Connection idle timeout |
66| Max origin connections | ~20 | ~100 | Connections to origin database |
67| Query duration max | 60s | 60s | Queries >60s terminated |
68| Cached response max | 50 MB | 50 MB | Responses >50MB returned but not cached |
69 
70## Resources
71 
72- [Docs](https://developers.cloudflare.com/hyperdrive/)
73- [Getting Started](https://developers.cloudflare.com/hyperdrive/get-started/)
74- [Wrangler Reference](https://developers.cloudflare.com/hyperdrive/reference/wrangler-commands/)
75- [Supported DBs](https://developers.cloudflare.com/hyperdrive/reference/supported-databases-and-features/)
76- [Discord #hyperdrive](https://discord.cloudflare.com)
77- [Limit Increase Form](https://forms.gle/ukpeZVLWLnKeixDu7)
78