On 6/6/06, David Corbin <[EMAIL PROTECTED]> wrote:
On Monday 05 June 2006 11:20 am, Charles O Nutter wrote:
> I tried a very naive version of this, just to demonstrate the performance
> gain.
>
> First off, if you never call cleanup during add, the size of the list will
> quickly grow to consume all memory. The objects the weakrefs point at will
> be collected, but the weakrefs themselves will not. Some cleanup is
> necessary during add, though it could probably only be run every N calls to
> add.
>
> If we ignore this, however, and increase the heap size to allow the list to
> grow, the performance gains moving to a list are still nowhere near
> eliminating OS entirely:
>
> For test: 1_000_000.times { <four literal strings> }
> normal run, 512M, OS as-is: 17.3s
> sync ArrayList, 512M, OS saves weakrefs: 16.4s
> sync ArrayList, 512M, OS saves objects: 22s
> unsync ArrayList, 512M, OS saves weakrefs: 16.2s
> unsync ArrayList pre-alloc 5M entries, 512M, OS saves weakrefs: 14.8s
> normal run, 512M, OS disabled: 7s
>
> So what does this tell us?
>
> First off, maintaining any sort of list is bad...ArrayList or otherwise.
> Even if we throw out things we need, like cleaning the list, and make the
> list huge to begin with, it's still over 2x as slow as not maintaining a
> list in the first place.
>
> Second, maintaining weakrefs is actually cheaper than maintaining the
> objects, probably because most of them are immediately collected in this
> contrived example.
>
> Third, it seems that nothing we do is going to reduce the cost of OS to an
> unnoticeable level. Look at it logically:
>
> Object Creation Without OS:
> - instantiate object (cheap)
> - set RubyClass (cheap if we reference builtin classes directly)
> - set tainting (cheap)
>
> Object Creation With OS:
> - all of the above plus...
> - list maintenance (potentially very expensive for a set or growing
> arraylist)
> - hashing (if using a set) (very expensive)
> - WeakRef creation (cheap)
> - cleanup (expensive)
>
> Even if we eliminate cleanup and hashing, we're still instantiating twice
> as many objects and maintaining a list.
>
> At this point, my vote goes to OS being disabled by default, with a flag to
> turn it on.
I'm sorry, but you must be joking. It's an integral part of what Ruby is.
Just about everyone that uses Test::Unit uses it for sure (even if they don't
kinow it), and who knows what other packages need it. I don't have any
specific answers for how to improve performance, but I don't think a switch
is good one.
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--
Charles Oliver Nutter @ headius.blogspot.com
JRuby Developer @ jruby.sourceforge.net
Application Architect @ www.ventera.com
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