Cookbook recipe

Connection pooling with PgBouncer (transaction vs session)

Applies to PostgreSQL 13–17 Last reviewed May 2026 Grounded in source

What This Is

A production experience capsule based on real incident patterns.

Why It Matters

Builds production judgment under pressure.

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Estimated investigation4 min

Scenario

Hundreds of app connections overwhelm PostgreSQL. PgBouncer multiplexes them onto a small pool of real backends. Diagnose it Count real backends vs app connections: SELECT count(*) FROM pg_stat_activity; SHOW max_connections; Why it happens Each PostgreSQL backend…

Investigation Path

Hundreds of app connections overwhelm PostgreSQL. PgBouncer multiplexes them onto a small pool of real backends.

Diagnose it

Count real backends vs app connections:

SELECT count(*) FROM pg_stat_activity;
SHOW max_connections;

Why it happens

Each PostgreSQL backend is a process with real memory cost. Thousands of mostly-idle app connections waste memory and scheduling. A pooler keeps a few warm backends and hands them out per transaction.

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Related & next steps

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Concepts on this page

Connection pooling Transaction
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