ruby/ruby on rails memory leak detection

A super simple method to log memory usage after or before each request (only for Linux).

#Put this in applictation_controller.rb
before_filter :log_ram # or use after_filter
def log_ram
  logger.warn 'RAM USAGE: ' + `pmap #{Process.pid} | tail -1`[10,40].strip
end

You might want to load up script/console and try the statement out first to make sure it works on your box.

puts 'RAM USAGE: ' + `pmap #{Process.pid} | tail -1`[10,40].strip

Then just monitor top, when a request makes your memory usage jump, go check the logs. This, of course, will only help if you have a memory leak that occurs in large jumps, not tiny increments.

Some tips to find memory leaks in Rails:

• use the Bleak House plugin
• implement Scout monitoring specifically the memory usage profiler
• try another simple memory usage logger

The first is a graphical exploration of memory usage by objects in the ObjectSpace.

The last two will help you identify specific usage patterns that are inflating memory usage, and you can work from there.

As for specific coding-patterns, from experience you have to watch anything that's dealing with file io, image processing, working with massive strings and the like.

I would check whether you are using the most appropriate XML library - ReXML is known to be slow and believed to be leaky (I have no proof of that!). Also check whether you can memoize expensive operations.