Author dmalcolm
Recipients Arach, Arfrever, Huzaifa.Sidhpurwala, Jim.Jewett, Mark.Shannon, PaulMcMillan, Zhiping.Deng, alex, barry, benjamin.peterson, christian.heimes, dmalcolm, eric.snow, fx5, georg.brandl, grahamd, gregory.p.smith, gvanrossum, gz, haypo, jcea, lemburg, mark.dickinson, merwok, neologix, pitrou, skrah, terry.reedy, tim.peters, v+python, zbysz
Date 2012-01-21.22:41:57
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On Sat, 2012-01-21 at 22:20 +0000, Antoine Pitrou wrote:

> Sounds a bit overkill, and it shouldn't be a public API (which
> __methods__ are). Even a private API on dicts would quickly become
> visible, since dicts are so pervasive.

Fair enough.

> > > > Caveats:
> > > > * no overflow handling (what happens after 2**32 modifications to a
> > > > long-lived dict on a 32-bit build?) - though that's fixable.
> > > 
> > > How do you suggest to fix it?
> > 
> > If the dict is heading towards overflow of these counters, it's either
> > long-lived, or *huge*.
> > 
> > Possible approaches:
> > (a) use 64-bit counters rather than 32-bit, though that's simply
> > delaying the inevitable
> 
> Well, even assuming one billion lookup probes per second on a single
> dictionary, the inevitable will happen in 584 years with a 64-bit
> counter (but only 4 seconds with a 32-bit counter).
> 
> A real issue, though, may be the cost of 64-bit arithmetic on 32-bit
> CPUs.
> 
> > (b) when one of the counters gets large, divide both of them by a
> > constant (e.g. 2).  We're interested in their ratio, so dividing both by
> > a constant preserves this.
> 
> Sounds good, although we may want to pull this outside of the critical
> loop.

OK; I'll look at implementing (b).

Oops, yeah, that was a typo; I meant 0 to disable.

> - 0 to disable it
> - 1 to enable it and use the default scaling factor
> - >= 2 to enable it and set the scaling factor

You said above that it should be hardcoded; if so, how can it be changed
at run-time from an environment variable?  Or am I misunderstanding.

Works for me.

> > BTW, presumably if we do it, we should do it for sets as well?
> 
> Yeah, and use the same env var / sys function.

Despite the "DICT" in the title?  OK.

Thanks for the feedback.
History
Date User Action Args
2012-01-21 22:41:58dmalcolmsetrecipients: + dmalcolm, lemburg, gvanrossum, tim.peters, barry, georg.brandl, terry.reedy, gregory.p.smith, jcea, mark.dickinson, pitrou, haypo, christian.heimes, benjamin.peterson, merwok, grahamd, Arfrever, v+python, alex, zbysz, skrah, gz, neologix, Arach, Mark.Shannon, eric.snow, Zhiping.Deng, Huzaifa.Sidhpurwala, Jim.Jewett, PaulMcMillan, fx5
2012-01-21 22:41:58dmalcolmlinkissue13703 messages
2012-01-21 22:41:57dmalcolmcreate