- Engineering
- Last Updated: November 05, 2025
- Richard Schneeman, Chap Ambrose
Puma 7 is here, and that means your Ruby app is now keep-alive ready. This bug , which existed in Puma for years, caused one out of every 10 requests to take 10x longer by unfairly “cutting in line.” In this post, I’ll cover how web servers work, what caused this bad behavior in Puma, and how it was fixed in Puma 7; specifically an architectural change recommended by MSP-Greg that was needed to address the issue.
- Engineering
- Last Updated: November 04, 2025
- Richard Schneeman, Chap Ambrose
The Performance Penalty of Repeated Connections
Before the latest improvements to the Heroku Router, every connection between the router and your application dyno risked incurring the latency penalty of a TCP slow start . To understand why this is a performance bottleneck for modern web applications, we must look at the fundamentals of the Transmission Control Protocol (TCP) and its history with HTTP.
Maybe you’ve heard of a keep-alive connection, but haven’t thought much about what it is or why they exist. In this post, we’re going to peel away some networking abstractions in order to explain what a keep-alive…
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