# Rails and CPU usage **URL:** \ **Category:** Rails\ **Created:** [October 23, 2007, 9:21pm UTC](https://www.ruby-forum.com/t/rails-and-cpu-usage/118099 "2007-10-23T21:21:01Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![RSElliott\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b487fb/32.png) [@RSElliott\_M](https://www.ruby-forum.com/u/RSElliott_M)\ **Post date:** [October 23, 2007, 9:21pm UTC](https://www.ruby-forum.com/t/rails-and-cpu-usage/118099/1 "2007-10-23T21:21:01Z")
I’ve had an app deployed for about six months now on Dreamhost and I’ve recently been paying attention to the daily CPU statistics my host provides. Since it’s a shared hosting environment there’s a semi-arbitrary amount of CPU minutes I am allowed to use before I’m told to pay for better hosting or find a better host. I’ve been kind of worried lately since my site has become more popular and as result, my CPU minutes are up. Here’s an excerpt from the log for yesterday: Process CPU seconds user machine count average dispatch.fcgi 1380.0600 90.150% 5.750% 229 6.026 Now based on Google Analytics that’s resultant from just under 900 unique visitors and 3,222 pageviews. So when I do the math it’s roughly 0.4CPU seconds per pageview. I’m really not sure when my host will have a problem; I’ve read that ~50-60 CPU minutes is sort of their limit (even though they claim they have none). I am at less than half that but I’m still fairly worried. I’m just wondering if this is typical of Rails. I have tried to consider what processes in my application might be CPU heavy but I can’t think of anything. The most intensive process I can think of would be thumbnailing uploaded images, which is really just a call directly to ImageMagick. My application is something like a forum (minus user registration) and is currently about 950 lines of code. ---
**Author:** ![RSElliott\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b487fb/32.png) [@RSElliott\_M](https://www.ruby-forum.com/u/RSElliott_M)\ **Post date:** [October 23, 2007, 9:31pm UTC](https://www.ruby-forum.com/t/rails-and-cpu-usage/118099/2 "2007-10-23T21:31:01Z")
I have to admit that, by and large, Rails is near the top of the CPU-usage chart of web frameworks. There is a lot of stuff that goes on behind the scenes, and a lot of stuff which I see in 2.0 they may have made into plugins. Also, your CPU chart will probably not show the CPU time spent in database queries, only handling them once they return. I have noticed a rather huge spike in the database engine on certain queries. I use PostgreSQL, and adding indexes helped a lot there. PostgreSQL is pretty smart when it comes to using an index, and will only use them when it feels there is both sufficient data in the table and you are selecting on rows it has an index for. In short, when PostgreSQL takes a lot of CPU, I find it’s my fault. 🙂 Page or fragment caching will also help a lot. If you can cache a fragment of code and be smart about when you re-render it, your CPU time should drastically decrease. For instance, I have (finally) started adding caching to my code, and currently cache purely “static” content, like a welcome page, or an about page. Granted, these are pretty easy pages to render to start with, but I had to start somewhere, and it was the easiest place. –Michael ---
**Author:** ![RSElliott\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b487fb/32.png) [@RSElliott\_M](https://www.ruby-forum.com/u/RSElliott_M)\ **Post date:** [October 24, 2007, 2:04am UTC](https://www.ruby-forum.com/t/rails-and-cpu-usage/118099/3 "2007-10-24T02:04:44Z")
> they’re displayed is conditional. I can only think to code my own > caching system, but that’s kind of outside of my knowledge. The only > solution I’ve found is memcached. The problem is memcached it > recommended only for massive sites. If it works for you though, use it. I don’t know your data set, but let’s say it’s under 5megs (which seems small enough your isp probably wouldn’t care). If by putting that all into memcache using keys that make sense to your app saves you from having to regenerate everything over and over, why not use it? Although conversely it wouldn’t be too hard to implement Cache.get, Cache.set, Cache.delete to work via the filesystem as well. Or the database. You can save a lot of cpu by avoiding rendering the templates… Perhaps you could also change the url structure to cache by user/conditions or something as well? ---
**Author:** ![RSElliott\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b487fb/32.png) [@RSElliott\_M](https://www.ruby-forum.com/u/RSElliott_M)\ **Post date:** [October 25, 2007, 4:12pm UTC](https://www.ruby-forum.com/t/rails-and-cpu-usage/118099/4 "2007-10-25T16:12:22Z")
I will have to do more research on memcached. The presentation I looked at for it said it was only used for very large websites with thousands of database rows, such as twitter. I figured that on my shared hosting environment, employing it might do more harm than good, but I honestly don’t know for sure either way. ---
**Author:** ![RSElliott\_M](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/b487fb/32.png) [@RSElliott\_M](https://www.ruby-forum.com/u/RSElliott_M)\ **Post date:** [October 24, 2007, 12:54am UTC](https://www.ruby-forum.com/t/rails-and-cpu-usage/118099/5 "2007-10-24T00:54:36Z")
Well, it’s good that it might not be my code slowing everything down, but at the same time bad that I can’t directly fix it. I guess if my site were commercial I could just “throw more hardware at it” but when it’s not for profit then that idea doesn’t work. At this point I’m making enough from ad revenue to maybe afford a VPS like slicehost. I’ve looked at caching but can’t really find anything that suits my needs. The records I’m pulling are the same for every user, but the way they’re displayed is conditional. I can only think to code my own caching system, but that’s kind of outside of my knowledge. The only solution I’ve found is memcached. The problem is memcached it recommended only for massive sites.