[Cuis-dev] Small dictionaries

[Luciano Notarfrancesco]

Great to know! I think you mentioned this before… you used it for method
dictionaries, right? I’ll make a note to look into this further, because in
modern computers it might have less of an impact, I should do benchmarks.


On Mon, Jan 12, 2026 at 21:01 Jan Vraný <Jan.Vrany at labware.com> wrote:

> On Mon, 2026-01-12 at 10:35 -0300, Juan Vuletich via Cuis-dev wrote:
> > Hi Luciano,
> >
> > On 2026-01-12 4:52 AM, Luciano Notarfrancesco via Cuis-dev wrote:
> > > In the software Iʼm currently programming Iʼm using the events
> > > subsystem a lot, and Iʼm subclassing from ActiveModel. Each model
> > > typically only triggers 2-3 types of events, so the action dictionary
> > > is very small. And I have another similar case with a small dictionary
> > > (also typically 2-3 entries, at most 5). Lookups and event triggering
> > > happen at about 300 Hz. Iʼm wondering, wouldnʼt be more efficient to
> > > just use arrays and a linear lookup instead of dictionaries? Or, has
> > > anyone implemented dictionaries optimized for a small number of
> > > entries? Any advice?
> > >
> > > In general, I think we donʼt have models that trigger many different
> > > types of events, so it seems this optimization could be used in
> > > ActionModel. But perhaps it hasnt been a priority to optimize this
> > > because we donʼt usually fire events at high rates, I guess.
> > >
> > > Thanks,
> > > Luciano
> >
> >
> > I think such optimization would belong in Dictionary. I mean, if a
> > Dictionary is small, it could use an alternative lookup method if that
> > improves performance. Having a different class would make use way more
> > complicated, and we'd need to keep an eye on whether we're using the
> > correct kind (small / large) all the time.
> >
> > Still, I doubt there would be any performance improvement. Especially in
> > IdentityDictionaries where the hash and equality are both quick
> > primitives, it looks like it would perform the same as today.
> >
> > Some benchmarking is in order, if you want to investigate.
>
> I did the benchmarking in the past. Expecially for small identity
> dictionaries
> it made a difference.
>
> It makes sense. If you organize small identity dictionary as a an array of
> alternating key/value, then you can squeeze 4 elements into a single
> cacheline.
>
> In that respect, the traditional smalltalk dictionary implementation using
> an
> array of associations is somewhat suboptimal. Simply one big array or
> having two arrays one with keys and other with values seems more
> cache-friendly.
>
> Jan
>
>
> >
> > Thanks,
> >
> > --
> > Juan Vuletich
> > http://www.cuis.st
> > http://github.com/jvuletich
> > http://researchgate.net/profile/Juan-Vuletich
> > http://independent.academia.edu/JuanVuletich
> > http://patents.justia.com/inventor/juan-manuel-vuletich
>
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