Sidekiq not deallocating memory after workers have finished

Question

I have about six Sidekiq worker which perform JSON crawling. Dependent on the endpoint's dataset size they finish between 1min and 4h. Especially, watching the long one, which takes 4h, I see a very slight increase of memory over time.

It's not a problem, until I want to schedule the same worker jobs again. The memory is not deallocated and stacks up, until I run into the Linux OOM Killer which gets rid of my Sidekiq process.

Memory leak? I watched the number of different objects in ObjectSpace:

ObjectSpace.each_object.inject(Hash.new(0)) { |count, o| count[o.class] += 1 } 

There is not really an increase there, the set of hashes, arrays, etc. stays the same, short increases are swept away by the Garbage Collector and gc.stat[:count] tells me, that the Garbage Collector is working, too.

Even after the worker finishes, e.g. I get the [Done] logged and no workers are busy any more, the memory is not deallocated. What are the reasons for that? Can I do something against this? Write a finalizer?

The only current solution: Restart the Sidekiq process.

I am on Ruby 2.0.0 and use Ruby MRI.

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For the JSON parsing I use Yajl, thus a C binding. I need it because it seems the only fast JSON parser that properly implements streamed reading and writing.

Answer 1

Mike Perham who wrote Sidekiq addressed this here: http://www.mikeperham.com/2009/05/25/memory-hungry-ruby-daemons/

tl;dr version: MRI will not give the memory back, the most you can do is control the heap, and to do that, Ruby Enterprise Edition was suggested.

Don't know that any of this helps, but that is the situation - straight from the horse's mouth.