How 7 Mongrels Handled a 550k Pageview Digging

http://shanti.railsblog.com/how-7-mongrels-handled-a-550k-pageview-digging

by sbraford • 19 years ago

20 18 19 years ago

shanti.railsblog.com

davidw4• 19 years ago

Here's what's annoying about Mongrel, summed up:

> As the title of this article suggests, only 7 mongrels were required to sustain the level of traffic. (this number was already set to seven before the digging, and didn't have to be increased)

Having to pick arbitrary numbers beforehand is a bad way of scaling. Apache with fcgid launches new processes as they're needed. It may not scale due to other problems, but "pick a number and pray" strikes me as a dubious idea.

mrtron2• 19 years ago

I am wondering why X mongrels are commonly used with Rails, is it just how mongrel is designed and dispatched that you need to establish X amount and it does not change with the load?

Being completely ignorant of mongrel, what is the benefit of having 7 mongrels running instead of 1? Does it not just do the job of dispatching the child processes to handle requests, so one would handle things just as effectively? I suppose what I am asking is, with one box why would you have more than one dispatcher?

socmoth2• 19 years ago

one mongrel handles one request. if you request takes one second to complete. you get one request/sec. 7 mongrels => 7 req/sec.

100req/sec * 7 mongrels => 700 req/sec total. and other simple math.

they aren't spawned automatically. you setup a number and distribute to them. there are ways of getting them to spawn automatically, but it isn't inherent to mongrel itself.

carpal3• 19 years ago

I really like the approach of having X number of processes started automatically. You can get really fine-grained in your scaling strategy, and can balance multiple projects on the same server much better than you could with Apache.

If you really want the "automatic blah blah blah" approach, you can always use fcgi with Apache. Many people do (including 37signals).

wmf• 19 years ago

One app server and one DB server counts as "scaling" now?

carpal3• 19 years ago

No, and the author never said it was.

PStamatiou• 19 years ago

i'm not much of a rails head but I did enjoy that article and it makes me happy that we're using nginx on http://Skribit.com

sbraford3• 19 years ago

Skribit looks sweet - is it RoR powered or what?

Are you in YCombinator?

luccastera• 19 years ago

I don't remember where I got the following snippet from so if someone knows, please point it out so that I can give them credit.

How many mongrels?

Here's a simple formula to follow:

A. Take the (average or median) request time, in seconds. Say, 0.250 seconds (250ms)

B. How many requests do you want to handle at peak? (e.g. 10,000 a minute, 166 a second)

C. Multiply A x B : 0.250 * 166 = 41.5

So you need about 40 mongrels to handle the load. At about 60MB per listener, that's 2.4GB of RAM, plus a bit of room for leakiness and swapping. Ezra at Engine Yard suggests "about 10 dogs per CPU core", which means that if we have a 4-core opteron box with 3GB of RAM, then this is possible on one box.

Your mileage will vary, which means, if the box is lagging, remove a few mongrels.

How 7 Mongrels Handled a 550k Pageview Digging

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