Cloud SQL: too many connections Google Cloud / Firebase Origin: Platform & cloud OSI layer 7 · Application Last updated 4 Nov 2026

Cloud SQL: FATAL: remaining connection slots are reserved / MySQL: ERROR 1040 (08004): Too many connections

The instance's maximum connections was reached, often because serverless instances each open their own connection pool.

Exact message you may see ERROR 1040 (08004): Too many connections Cloud SQLToo many connections Cloud SQLFATAL: sorry, too many clients already Cloud SQL
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Seen on: Google Cloud SQL

Meaning

Cloud Run/Functions scale out and each instance opens connections. Set small pools (1-5 per instance), use connection pooling (PgBouncer / managed connection pooling), lower max-instances, and close idle connections. Raise max_connections flag only after sizing memory.

Common causes

  • Many serverless instances each with a pool
  • Pool max size too large
  • Connections never closed/leaked
  • Low max_connections on a small tier
  • Long-running transactions holding slots

⚡ Quick fix

  1. Limit pool size per instance (e.g. 2-5) and instances
  2. Use managed connection pooling or PgBouncer
  3. Increase max_connections and instance size if justified

Detailed fix by platform

gcloud

  1. gcloud sql instances patch INSTANCE --database-flags=max_connections=300

How to diagnose

  1. Count — Connections vs max?
  2. Source — Instances x pool?
  3. Leaks — Idle connections?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Platform & cloud. Errors that are often confused with or caused by this one (click to open):

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