[Numpy-discussion] searchsorted() and memory cache

Charles R Harris charlesr.harris@gmail....
Wed May 14 18:27:58 CDT 2008


On Wed, May 14, 2008 at 2:00 PM, Andrew Straw <strawman@astraw.com> wrote:

> Charles R Harris wrote:
> >
> >
> > On Wed, May 14, 2008 at 8:09 AM, Andrew Straw <strawman@astraw.com
> > <mailto:strawman@astraw.com>> wrote:
> >
> >
> >
> >     Quite a difference (a factor of about 3000)! At this point, I haven't
> >     delved into the dataset to see what makes it so pathological --
> >     performance is nowhere near this bad for the binary search algorithm
> >     with other sets of keys.
> >
> >
> > It can't be that bad Andrew, something else is going on. And 191 MB
> > isn's *that* big, I expect it should bit in memory with no problem.
> I agree the performance difference seems beyond what one would expect
> due to cache misses alone. I'm at a loss to propose other explanations,
> though. Ideas?


I just searched for  2**25/10 keys in a 2**25 array of reals. It took less
than a second when vectorized. In a python loop it took about 7.7 seconds.
The only thing I can think of is that the search isn't getting any cpu
cycles for some reason. How much memory is it using? Do you have any nans
and such in the data?

Chuck

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