How many simultanious users

Laurence Rowe l at
Wed Aug 12 16:41:01 CEST 2009

Remember to up the ulimit -n, with http keep-alive you can quickly run
into the linux default of 1024 open files/sockets.


2009/7/16 Lazy <lazy404 at>:
>>>> assuming that each user loads 40 files in 1 minute we get
>>>> 12000*60/40=18 000 users per minute
>>>> Is it possible to get half of that 18k users/per minute in real word
>>>> ignoring the amounts of traffic it will generate ?
>>> I'd say so, but it depends on how big the data set is. If you can store it
>>> in memory, varnish is ridiculously fast. I also wouldn't recommend relying
>> i think it will fit in to ram, i will be a single site
>>> on a single Varnish for more than a few thousand requests per second. If
>>> something goes wrong (suddenly getting lots of misses for instance), it
>>> will quickly spread.
>>> For comparison, I'm looking at a box with roughly 0.4 load serving
>>> 2000req/s as we speak, and that's on 2xDual Core Opteron 2212. Going by
>>> those numbers, it should theoretically be able to handle almost ten times
>>> as many requests if Varnish scaled as a straight line.
>>> That'd give you roughly 18000 req/s at peak (give or take a little...) Now
>>> you're talking about 8 cores, that should be 36k req/s. That's _not_
>>> unrealistic, from what we've seen in synthetic tests. If each client
>>> requires 40 items, that means roughly 900 clients _per second_. Or 54k in a
>>> minute. This math is all rough estimates, but the foundation is production
>>> sites and real traffic patterns.
>>> The problem is that getting your Varnish to deal with 36k req/s is rather
>>> difficult, and you quickly run into network issues and similar. And at 36k
>>> req/s you can hardly take any amount of backend traffic or delays before it
>>> all falls over.
> today i did some ad-hoc tests with 45 byte body,
> when I enable keep-alive I'm getting 39k req/s with 100 concurrent
> gets and over 40k with 300 concurrent connections (max cpu load was
> under 2 cores for varnish)
> without keep alive i'm stuck with 12k req/s, that might be end of ab's
> performance in making new connections or
> kernel, i tried the performance tips from the wiki, but id didn't make
> a significant difference in this test,
> Later i will try to use a benchmark running on another machine.
> 12k req/s is more then enough for me already so I'm happy with that
> --
> Michal Grzedzicki
> _______________________________________________
> varnish-misc mailing list
> varnish-misc at

More information about the varnish-misc mailing list