Regarding memory allocation -- it seems like it might be a bug in the
@allocated macro rather than an actual indication of memory usage.
When I run
a = rand(100000)
@allocated sort(a, by=x->x)
I get 768403668 which is 768 MB.
However, I was also recording the process's memory usage using %mem. For my
16 GB machine, the usage initially is 0.5% and jumps to 1.3% after running
the above two commands which comes to around ~200MB rather than 768MB.
While that's still a high jump compared to the array size (which is only
~8MB), that might be because of the way VM allocates more memory. Perhaps
someone who's more familiar with the internals can comment.
On Sunday, July 6, 2014 7:30:47 AM UTC-4, gentlebeldin wrote:
>
> No, that wasn't the reason, in this case. I had another, hard look at my
> own (rough and ready) implementation of factoring, found a rather stupid
> mistake, and now, it runs in 2.2 seconds.
> Using List<Integer> or List<Double> instead of int[] or double[] for
> numerical computations would be a silly idea, indeed, and not just because
> of poor performance. It would also eat up lots of memory. In this case, I
> had to sort a big array of integers (100,000,000 elements), with a custom
> comparator. That isn't possible with Java's int[], and Integer[] with so
> many elements is a bit harsh for a netbook with 2 GB of RAM. Then, I
> thought "hey, I can implement the List<Integer> interface with an int[]!"
> No such luck, the implementation of Collections.sort calls toArray, first,
> ->Integer[] :-(
> Then, they introduced streams in Java 8, including IntStream, a stream of
> ints, for better performance, and defined the corresponding functional
> interface for a custom comparator. That sounds promising, but as we know,
> most promises aren't kept. Believe it or not, the implementation of
> IntStream.sort collects the whole stream in an Integer[], first. :-(
> That's why I put some hope into Julia. Unfortunately, it may allocate huge
> amounts of memory in an unpredictable way (for me, at least), too.
>
> Am Sonntag, 6. Juli 2014 07:12:26 UTC+2 schrieb Sid:
>>
>> Are you using Integer/Double objects by any chance in Java? I've found
>> using them to be a surefire way of destroying Java's performance...
>>
>> On Saturday, July 5, 2014 3:11:47 AM UTC-4, gentlebeldin wrote:
>>>
>>> It's hard to tell for sure, I wouldn't know how to check that. I prefer
>>> to port a few more solutions. My curiosity was much increased by this one:
>>>
>>> julia> include("julia/jl/e443gcd.jl")
>>> elapsed time: 3.255950529 seconds (929628 bytes allocated)
>>>
>>>
>>> The Java original "runs" much longer, 33 seconds.
>>>
>>>
>>>>
