Moves On Rails: Nested include has major memory leak (Rails 2.0.1).

Nested include has major memory leak (Rails 2.0.1).

bart.tenbrinke@movesonrails.com (Bart ten Brinke) — Wed, 02 Jul 2008 15:59:00 +0200

As our mongrels were using up quite a lot of memory, so I tried to figure out what was causing this.

When running the app locally I found out that one certain page caused the mongrel to grow from 60 to 190 megabytes. A whopping 130 megabytes!

After commenting out some of the code, I realized that a single line was causing all of the memory usage

contracts = Contract.find( :all, 
  :conditions => ['contracts.employee_id IN (?) ', employees ],
  :include => [:expertise_profile => :qualifications ] )

Ouch! The nested include of rails somehow leaks a large amount of memory. The fix was a piece of cake.

contracts = Contract.find( :all, 
  :conditions => ['contracts.employee_id IN (?) ', employees ],
  :include => :expertise_profile )

Now my mongrel stays at 60 megabytes. I don't know if this issue persists in the new 2.1 Rails, but I'll check that soon!

"Nested include has major memory leak (Rails 2.0.1)." by Matt Griffith

Fri, 15 Aug 2008 04:27:35 +0200

Thanks for posting this. I'm seeing the same thing even when using a non-nested :include. I have an :include that loads 6 associations and it has a similar leak. This is in 2.0.2, I haven't tested 2.1 yet.

"Nested include has major memory leak (Rails 2.0.1)." by Bart ten Brinke

Fri, 15 Aug 2008 00:08:24 +0200

You are correct Steve, but normally after a request, the mongrel should return to its normal memory footprint, which in this case it does not. The footprint grew 130 MB which is only returned when you restart the mongrel.

"Nested include has major memory leak (Rails 2.0.1)." by Steve Root

Tue, 05 Aug 2008 17:07:14 +0200

I'm new to rails, but isn't the difference here that you are no longer (eager) loading the qualifications table into the model? The less data you load, the smaller the memory used

"Nested include has major memory leak (Rails 2.0.1)." by Jon Dahl

Wed, 02 Jul 2008 17:21:11 +0200

Great catch. Be sure to post again if you find out anything more (like: if 2.1 has the same problem, or the underlying cause of the leak).