Question

I am writing a ruby on rails application and one of the most important featuers of the website is live voting. We fully expect that we will get 10k voting requests in as little as 1 minutes. Along with other requests that means we could be getting a ton of requests.

My initial idea is to set up the server to use apache + phusion, however, for the voting specifically I’m thinking about writing a php script on side and to write/read the information in memcached. The data only needs to persist for about 15 minutes, so writing to the database 10,000 times in 1 minute seems pointless. We also need to mark the ip of the user so they don’t vote twice thus being extra complicated in memcached.

If anyone has any suggestions or ideas to make this work as best as possible, please help.

Answer 1

If you’re architecting an app for this kind of massive influx, you’re going to need to strip down the essential components of it to the absolute minimum.

Using a full Rails stack for that kind of intensity isn’t really practical, nor necessary. It would be much better to build a very thin Rack layer that handles the voting by making direct DB calls, skipping even an ORM, basically being a wrapper around an INSERT statement. This is something Sinatra and Sequel, which serves as an efficient query generator, might help with.

You should also be sure to tune your database properly, plus run many load tests against it to be sure it performs as expected, with a healthy margin for higher loading.

Making 10,000 DB calls in a minute isn’t a big deal, each call will take only a fraction of a millisecond on a properly tuned stack. Memcached could offer higher performance especially if the results are not intended to be permanent. Memcached has an atomic increment operator which is exactly what you’re looking for when simply tabulating votes. Redis is also a very capable temporary store.

Another idea is to scrap the DB altogether and write a persistent server process that speaks a simple JSON-based protocol. Eventmachine is great for throwing these things together if you’re committed to Ruby, as is NodeJS if you’re willing to build out a specialized tally server in JavaScript.

10,000 operations in a minute is easily achievable even on modest hardware using a specialized server processes without the overhead of a full DB stack.

You will just have to be sure that your scope is very well defined so you can test and heavily abuse your implementation prior to deploying it.

Since what you’re describing is, at the very core, something equivalent to a hash lookup, the essential code is simply:

contest = @contest[contest_id]

unless (contest[:voted][ip])
  contest[:voted][ip] = true
  contest[:votes][entry_id] += 1
end

Running this several hundred thousand times in a second is entirely practical, so the only overhead would be wrapping a JSON layer around it.