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Why Sizing Your Database Connection Pool Is Completely Counter-Intuitive
If your web service starts running out of database connections during a traffic spike, your first instinct is probably to increase the pool limit: go from 100 to 300 or 500 connections.
It seems logical. If 100 workers are busy, surely adding 400 more workers will let the database process more queries at the same time.
In database engineering, this intuition is completely backward.
Increasing connection pool sizes beyond your hardware limits doesn’t increase throughput — it collapses it. When you configure hundreds of connections on an 8-core database server, queries that normally take 3 milliseconds begin taking 8 seconds, and your database CPU locks at 100%.
The reality of systems performance is counter-intuitive: smaller connection pools consistently deliver higher throughput and lower latency than large ones.
Here is the benchmark data that explains why, how operating system threads actually execute on physical hardware, and the exact formula to size your pool correctly.
1. What Happens When You Open a Database Connection?
Many developers assume a database connection is just a lightweight memory pointer. In reality, establishing and maintaining a database socket is a heavy operating system operation:
[Web Application Pod] [PostgreSQL Database…
