What is a database connection pool?

A pool is a cache of reusable database connections. Instead of opening a new connection for every query, the app borrows one from the pool and returns it when done.

How do I check active database connections?

In PostgreSQL: SELECT count(*) FROM pg_stat_activity; In MySQL: SHOW PROCESSLIST; These show all active connections and their states.

Fix Database Connection Pool Exhausted — Resolve Connection Limits

Direct answer

Database connection pool exhaustion occurs when all connections are in use and no new connections can be acquired. This is typically caused by connection leaks in error handling paths or undersized pool configuration. Audit connection release logic and increase pool size.

Structured breakdown

Cause

Connection pool exhaustion happens when your app opens more connections than it releases. Check for connection leaks in error paths, increase pool size to match your database's max_connections, and add idle timeout settings.

Fix

Audit code for connection leaks ensure connections are released in finally blocks
Increase pool size to accommodate peak concurrent request volume
Set idle connection timeout to automatically reclaim unused connections

Outcome

Queries execute without connection errors and pool utilization stays within limits.

Common causes

Connection leaks — connections not released after errors
Pool size too small for the number of concurrent requests
Long-running transactions holding connections open
Missing connection idle timeout configuration
Multiple services sharing the same database without coordinated pool limits

Fix steps

1
Audit code for connection leaks ensure connections are released in finally blocks
2
Increase pool size to accommodate peak concurrent request volume
3
Set idle connection timeout to automatically reclaim unused connections
4
Break up long-running transactions into smaller units of work
5
Monitor active connection count and alert when approaching the limit

Analyze this issue

Paste the issue description, logs, or symptoms into the fix tool to inspect this problem with your own runtime details.

kintify fix

Need more context?

If the standard steps do not resolve the issue, open the fix tool and include the current logs, configuration, and deployment changes.

Open Fix Tool

Frequently asked questions

These examples show the commands, logs, and configuration patterns most often used to verify this issue.

Command examples

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

Log snippet

ERROR: remaining connection slots are reserved for non-replication superuser connections
pool: timeout expired, all connections in use (active: 100, idle: 0)

Config snippet

# postgresql.conf
max_connections = 200

# Application pool config
pool.max = 20
pool.min = 5
pool.idleTimeoutMillis = 30000