ActiveRecord memory leak with multiple threads?

gistfile1.rb

# It appears that when I perform a query with AR via multiple threads,
# the instantiated objects do not get released when a GC is performed.

threads = Array.new(5) { Thread.new { Foo.where(:status => 2).all.first(100).each { |f| f.owner.first_name } } }
threads.each(&:join)
threads = nil

GC.start

ObjectSpace.each_object(Foo).count # => instances still exist

# ----------------

Foo.where(:status => 2).all.first(100).each { |f| f.owner.first_name }

GC.start

ObjectSpace.each_object(Foo).count # => 0

Thank you @mboeh. That's very interesting and very good to know!

Things in ObjectSpace are not necessarily live instances. There are shortcut tricks you can use to force memory to be free'd / overwritten (in MRI only, where it's full of hacks at the C level "for speed"). Assuming that any Ruby GC will be fully deterministic around GC.start behavior is unlikely to be productive.