Neon "Remaining Connection Slots Are Reserved" (Too Many Connections)

How to fix it

Try these in order — the most common fix is first.

1. 1. Use the pooled connection string

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   1. In the Neon Console click Connect and enable Connection pooling
   2. Use the host that contains -pooler in the app's DATABASE_URL
   3. PgBouncer accepts up to 10,000 client connections
   Did this fix it? Yes No

2. 2. Close idle and long-running connections

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   1. Reuse a single client or pool per process
   2. Find stuck sessions with SELECT * FROM pg_stat_activity; and end them
   Did this fix it? Yes No

3. 3. Increase compute size

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   1. Project, Branches, Edit compute, raise the max CU
   2. Larger computes allow more connections (4000 cap at 9 CU and above)
   Did this fix it? Yes No

4. 4. Pooling already on?

   1. Contact Neon Support about raising default_pool_size
   Did this fix it? Yes No

Symptoms

Error: 'remaining connection slots are reserved for roles with the SUPERUSER attribute', often in serverless functions under load.

Why it happens

• Serverless functions each open their own direct connection
• max_connections scales with compute size (112 on 0.25 CU, 450 on 1 CU, 901 on 2 CU)
• Leaked or idle connections in the app

This guide also covers

• neon too many connections
• neon remaining connection slots are reserved
• neon pooler connection limit

The same problem in other apps

All not loading, error messages & connection guides →

• Supabase Max Client Connections Reached (Supabase)
• PlanetScale Prisma Connection Errors (PlanetScale)
• Railway SSL Certificate Stuck or Not Working (526, 525, Too Many Redirects) (Railway)

Other Neon errors

• Neon Connection Timeout After Scale to Zero (Cold Start)
• Neon Compute Time Quota Exceeded (Free Plan Limit Reached)
• Neon Free Plan Storage Limit Reached (Writes Blocked)
• Neon Cannot Create Branch: Branch Limit Reached
• Neon Prisma or Drizzle Migration Fails (Pooled Connection)
• Neon SSL Required Error (Connection Is Insecure)
• Neon "The Endpoint ID Is Not Specified" / Password Authentication Failed
• Neon "Active Endpoints Limit Exceeded" / Compute Suspended