Ruby On Rails is slow...?

Question

I'm writing a web application to monitor a furniture factory production flow. It has thousand of data to handle. So far, I run RoR on Mongrel + MySQL and it's really really slow (2-4min for some views). When I look at RoR logs, it seems that database queries aren't slow (0-10ms).

Is RoR slow when it converts database data to object? Is Mongrel slow?

Edit: First thing: I was in dev. env. In the production environment, the slowest view takes 2min (which would turn down to less than 1min on a good computer, mine is 5 years old). With ruby-prof and a bit of common sense, I've found out which methods were slowing down the application. The problem is that single SQL queries are called in loops on larges datasets:

ofs = Ofkb.find_by_sql ["..some large SQL query..."]

for of in ofs # About 700-1000 elements
   ops = Operation.find(..the single query..)
   etc.
end

Here are ruby-prof results on those methods:

 %self     total     self     wait    child    calls  name
 32.19     97.91    97.91     0.00     0.00       55  IO#gets (ruby_runtime:0}
 28.31     86.39    86.08     0.00     0.32    32128  Mysql#query (ruby_runtime:0}
  6.14     18.66    18.66     0.00     0.00    12432  IO#write (ruby_runtime:0}
  0.80      2.53     2.42     0.00     0.11    32122  Mysql::Result#each_hash (ruby_runtime:0}

The problem is: I can't really avoid those single queries. I've got thousands of events from which I have to compute complex data. Right now I'm using memcached on those methods which are OK unless you're the first to request the page.

Answer 1

I'll agree with everyone else. You have to profile. There is no point in doing anything to your code until you know what specifically is causing the slowness. Trying to fixing a problem without understanding the cause is like feeling ill and deciding to have lots of surgery until you feel better. Diagnose your problem first. It might be something small like a network setting or it could be one bad line in your code.

Some tips for profiling:

How to Profile Your Rails Application

Performance Testing Rails Applications

At the Forge - Profiling Rails Applications

Once you have found the bottleneck you can figure out what to do.

I recommend these videos: Railslab Scaling Rails

Revised now based on prof results:

OK. Now that you can see that your problem is that you are doing some sort of calculation using a query based on looping through the results of another active record query I'd advise you to look into building a custom SQL statement combining your initial selection criteria and the loop calculation to get what you need. You can definitely speed this up by optimizing the SQL.