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by mr_toad 656 days ago
Stack overflow absolutely had load balancers, and 9 web servers, and Redis caches. They also use 4 SQL servers, so not entirely vertical either. And they were only serving 500 requests a second on average (peak was probably higher).
1 comments
pajeets 656 days ago
was it? i read it was a huge ram server
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zo1 656 days ago
The details of their architecture is documented in a series of blog posts:

https://nickcraver.com/blog/2016/02/03/stack-overflow-a-tech...

I get what you're saying, they didn't do dynamic and "wild" horizontal scaling, they focused more on having an optimal architecture with beefy "vertically scaled" servers.

Very much something we should focus on. These days horizontal scaling, microservices, kubernetes, and just generally "throwing compute" at the problem is the lazy answer to scaling issues.

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mr_toad 656 days ago
https://stackexchange.com/performance
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DoctorOW 656 days ago
That's a primary and backup server for Stackoverflow and a primary/backup for SE. But they each have the full dataset for their sites, not actual horizontal scaling. Also that page is just a static marketing tool, not very representative of their current stack. See: https://meta.stackexchange.com/questions/374585/is-the-stack...
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KronisLV 653 days ago
Having most of the servers be loaded at about 5% CPU usage feels extremely wasteful, but at the same time I guess it's better to have the spare capacity for something that you really want to keep online, given the nature of the site.

However, if they have a peak of 450 web requests per second and somewhere between 11000 - 23800 SQL queries per second, that'd mean between 25 - 53 SQL queries to serve a single request. There's probably a lot of background processes and whatnot (and also queries needed for web sockets) that cut the number down and it's not that bad either way, but I do wonder why that is.

The apps with good performance that I've generally worked with attempted to minimize the amount of DB requests needed to serve a user's request (e.g. session cached in Redis/Valkey and using DB views to return an optimized data structure that can be returned with minimal transformations).

Either way, that's a quite beefy setup!

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