Hi Levente,

>       > That's better, but it still has that same fundamental problem.
> Every time a developer makes a HashedCollection of a known-at-runtime size
> (e.g., in a variable), they're forced to choose between execution
> performance pain or code pain.
> >       >
> >       >     {
> >       >    '[ Dictionary new ]'->'100% of baseline rate, 27,600,000 per
> second. 36.2 nanoseconds per run. 11.33547 % GC time.'
> >       >
> >       >     "performance pain?"
> >       >     '[ Dictionary new: 1 ]'->'60% of baseline rate, 16,600,000
> per second. 60.1 nanoseconds per run. 5.61888 % GC time.'
> >       >     '[ Dictionary new: 2 ]'->'61% of baseline rate, 16,900,000
> per second. 59.2 nanoseconds per run. 5.67886 % GC time.'
> >       >     '[ Dictionary new: 3 ]'->'59% of baseline rate, 16,300,000
> per second. 61.5 nanoseconds per run. 6.77864 % GC time.'
> >
> >       Even if there's a performance overhead, you use less memory.
> >
> >
> > But #new: is about optimization along *both* of those dimensions.
> Imagine how complicated a "manpage" for #new: would have to be if it
> weren't.  #new: must _never_ perform significantly worse than #new (for
> sizes <= the default), because it would either trick or force developers
> into writing less-performant
> > code, or into acknowledging Squeak's internal Dictionary implementation
> in their own code.  It feels like an API-design bug.
>
> It was okay for quite a long time. :)
>

... until this proposal which changed the smallest internal array size from
5 to 3 and introduced the above anomaly.  I assume you made that change
because you felt something else *wasn't* okay (to which I agree!).


>
> >
> >        >     "into #sizeFor:"
> >
> >       >     '[ Dictionary new: 4 ]'->'57% of baseline rate, 15,800,000
> per second. 63.5 nanoseconds per run. 7.87685 % GC time.'
> >
> >       Starting from 4, you also save time by avoiding growing, which is
> >       more significant than what you "lose" during instance creation.
> >
> >
> > Except my Dictionary is never going to grow.
>
> So, we actually say the same thing.
>

Did we?  You were arguing about saving time with growing, which I can never
gain.  I only lose during instance creation...


> > In case it helps bring clarity, my scenario is the GraphQL server.  As a
> Request comes in, the server will know, depending on the type, how many
> named arguments to expect (for most "normal" schema's, 0 to 4, but it can
> define any number it wants).  So it creates right sized Dictionary to hold
> them all, and will
> > never grow beyond that.  I simply don't want the server to have to do
> extra work when **vast majority** of requests will have fewer than 4
> arguments.
> >
> >       We could get rid of the anomaly by changing #new to ^self new: 3.
> >
> >
> > Yes, I'd be fine with that solution, too!   For me, it's only about
> violation of #new:'s contract.
>
> I don't see any broken contract here. It may be surprising to see
> somewhat worse performance with #new: than with #new (25 nanoseconds per
> instance according to your measurements),


a 40% hit...


> but both of those methods do
> what they should. Just because there was an easy optimization applied to
> #new, nothing was broken IMHO.
>

... for using #new: that's *supposed* to be for optimization!

So if you were in my shoes (which, if this goes to trunk as-is eventually
you will be!), would you take a 40% hit in performance-critical code
needing to instantiate a Dictionary with:

    Dictionary new: runtimeSize

Or, actually violate encapsulation to preserve performance?

   sz>3 ifTrue: [Dictionary new: sz] ifFalse: [Dictionary new]

?

My past observations have been that you like and appreciate the
most-efficient performing code, so I'm truly curious!

Best Regards.
  Chris
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