Scaling Slack and GitHub with Maude Lemaire

ℹ️ EPISODE INFO

Released

November 5, 2026

Duration

1h 19m

Channel

The Pragmatic Engineer

Watch on YouTube

▶ Open ↗

📝 EPISODE DESCRIPTION

What is involved in scaling up large, popular products at places like Slack and GitHub? We get an insider’s view on this from Maude Lemaire, a principal engineer and author of ‘Refactoring at Scale: Regaining Control of Your Codebase.’ She spent nearly eight years at Slack, where she led the backend performance infrastructure team, before joining GitHub to tackle database scaling challenges. Most recently, she worked on improving performance at Cursor – including time to first token. In this episode of The Pragmatic Engineer, Maude and I dig into the challenges of scaling some of the world's largest software products. We explore how Slack handled growing numbers of enterprise customers, how it evolved its approach to load testing, and the lessons Maude learned during nearly eight years of scaling Slack's infrastructure. She also tells us what it was like joining GitHub in 2024 when Copilot was taking off, the challenges of working with GitHub's gigantic Rails monolith, and how Maude uses AI in her work – while keeping judgment calls and decision-making firmly in her own hands. — *Brought to you by:*

• Antithesis – verify your system’s correctness without human review or traditional integration tests – and avoid bugs or outages. https://antithesis.com/pragmatic
• turbopuffer – a vector and full-text search engine built on object storage. It’s fast, cheap, and extremely scalable. https://turbopuffer.com/pragmatic
• Entire – The Git forge for agent-human collaboration. Built for the scale and throughput of agentic coding. http://entire.io/pragmatic

— *The Pragmatic Engineer deepdives relevant for this episode:*

• Real-world engineering challenges: building Cursor https://newsletter.pragmaticengineer.com/p/cursor
• Pushing software engineering limits with “napkin math” https://newsletter.pragmaticengineer.com/p/pushing-software-engineering-limits
• What is happening with code reviews? https://newsletter.pragmaticengineer.com/p/what-is-happening-with-code-reviews
• Why reliability is hard at scale: learnings from infrastructure outages https://newsletter.pragmaticengineer.com/p/why-reliability-is-hard-at-scale
• What is Reliability Engineering? https://newsletter.pragmaticengineer.com/p/reliability-engineering
• Migrations Done Well https://newsletter.pragmaticengineer.com/p/migrations
• Shipping to Production https://newsletter.pragmaticengineer.com/p/shipping-to-production
• The Platform and Program Split at Uber https://newsletter.pragmaticengineer.com/p/program-platform-split-uber
• The present, past and future of GitHub https://newsletter.pragmaticengineer.com/p/github
• Why performant code matters (but gets widely ignored), with Casey Muratori https://newsletter.pragmaticengineer.com/p/why-performant-code-matters-but-gets
• Designing Data-intensive Applications with Martin Kleppmann https://newsletter.pragmaticengineer.com/p/designing-data-intensive-applications

— *Where to find Maude Lemaire:*

• X: https://x.com/QcMaude
• LinkedIn: https://www.linkedin.com/in/lemairemaude
• Website: https://maudethecodetoad.com

— *In this episode, we cover:* 00:00 Intro 03:15 Early years and path to software engineering 07:32 First job at Rent the Runway 09:17 The HipChat data leak 10:54 Joining Slack and the challenges of scaling 26:30 Load testing and thundering herds 32:29 Event floods 38:30 Evolving load testing at Slack 48:38 Joining GitHub in 2024 56:52 The challenges of the Rails monolith 1:02:26 How Maude uses AI 1:12:40 Advice for engineers interested in product/platform work — See the transcript and other references from the episode at https://newsletter.pragmaticengineer.com/podcast — Production and marketing by https://penname.co/.

🎤 SPEAKERS

• Maude Lemaire

  guest

  Principal software engineer and author of "Refactoring at Scale," with engineering experience at Slack and GitHub.

• Gergely Orosz

  host

  Software engineer and writer behind The Pragmatic Engineer, hosting interviews on software engineering and scaling systems.

🧾 EPISODE SUMMARY

In this episode of The Pragmatic Engineer, featuring Maude Lemaire and Gergely Orosz, Scaling Slack and GitHub with Maude Lemaire explores Inside Slack and GitHub scaling: WebSockets, sharding, Rails, AI Maude Lemaire describes scaling challenges at Slack, including failure modes like thundering herds and client-side event floods driven by WebSocket fanout and downstream reads.

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