question.md

id	73
title	Database Connection Pooling
category	Databases
topics	connection pool PgBouncer sizing Postgres
difficulty	Medium
solution	solution.md

Problem 73, Database Connection Pooling

Scenario: A team's Postgres database keeps hitting "too many connections" errors during traffic spikes. The error is intermittent; under normal load the app is fine. Someone proposes "raising max_connections from 100 to 1000." You suspect that is the wrong fix.

In the interview, the question is:

Why does connection pooling exist, how do you size a pool, and why is raising max_connections rarely the right answer?

---

Your Task:

1. Explain what a Postgres connection costs.
2. Define a connection pool.
3. Walk through sizing.
4. Cover where the pool lives (app side vs proxy side).

---

What a Good Answer Covers:

• Backend process per connection in Postgres.
• Memory and CPU cost per connection.
• PgBouncer and similar proxies.
• Transaction vs session pooling.
• How to compute a reasonable size.