Scenario

Your API service starts throwing 500 errors. The logs say FATAL: remaining connection slots are reserved for non-replication superuser connections.

Question

What is happening, and how do you fix it (short term and long term)?

Expected Answer

1. Root Cause: The application has exhausted the Postgres max_connections limit.
2. Short Term Fix:
   • Restart app pods (clears leaked connections).
   • Temporarily increase max_connections if RAM allows.
3. Long Term Fix:
   • Implement client-side pooling (e.g., HikariCP) properly.
   • Use a server-side pooler like PgBouncer to multiplex connections.
   • Check for connection leaks (code not closing rows/sessions).