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Fix "Too many connections" database errors

ERROR 1040: Too many connections (MySQL) or remaining connection slots are reserved (PostgreSQL) means your app opened more database connections than the server allows. Raising the limit is the last fix — first stop leaking connections.

Why it happens

A database allows a fixed number of simultaneous connections. You hit the ceiling when:

  • Connections aren’t released — the app opens a new one per request and never closes it (the #1 cause).
  • No connection pooling — every request/worker makes its own direct connection.
  • Too many app workers/processes each holding connections.
  • A traffic spike genuinely needs more than the limit allows.

Diagnose

MySQL:

SHOW STATUS LIKE 'Threads_connected';
SHOW PROCESSLIST;          -- who's connected, and are they idle?

PostgreSQL:

SELECT count(*) FROM pg_stat_activity;
SELECT state, count(*) FROM pg_stat_activity GROUP BY state;

Lots of idle connections = a leak or missing pooling.

Fix it properly (in order)

  1. Use a connection pool. Almost every framework supports one — a small pool (e.g. 5–10) reused across requests beats one-per-request. This fixes most cases.
  2. Close connections you open manually, including on error paths.
  3. Right-size your workers. workers × pool-size must stay under the DB limit. Twenty workers each with a pool of 10 = 200 connections — plan for it.
  4. Then, if genuinely needed, raise max_connections — but more connections use more memory, so pooling is almost always the better lever.

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