On most UNIX systems this will leave a large unallocated virtual "hole" in the
file. If you are not bothered by spreading the allocation task out over the
program execution interval, this won't matter and will probably give the best
performance. However, if you wanted to benchmark your algorithms without the
erratic filesystem updates mixed in, then you need to write all of those
zeroes. For that to work most efficiently, write data in large blocks, and if
possible bypass the C standard library.
---------------------------------------------------------------------------
Jeff Newmiller The ..... ..... Go Live...
DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live Go...
Live: OO#.. Dead: OO#.. Playing
Research Engineer (Solar/Batteries O.O#. #.O#. with
/Software/Embedded Controllers) .OO#. .OO#. rocks...1k
---------------------------------------------------------------------------
Sent from my phone. Please excuse my brevity.
Simon Urbanek <simon.urba...@r-project.org> wrote:
>
>On May 2, 2012, at 6:23 PM, Jonathan Greenberg wrote:
>
>> R-helpers:
>>
>> What would be the absolute fastest way to make a large "empty" file
>(e.g.
>> filled with all zeroes) on disk, given a byte size and a given number
>> number of empty values. I know I can use writeBin, but the "object"
>in
>> this case may be far too large to store in main memory. I'm asking
>because
>> I'm going to use this file in conjunction with mmap to do parallel
>writes
>> to this file. Say, I want to create a blank file of 10,000 floating
>point
>> numbers.
>>
>
>The most trivial way is to simply seek to the end and write a byte:
>
>> n=100000
>> f=file("foo","wb")
>> seek(f,n-1)
>[1] 0
>> writeBin(raw(1),f)
>> close(f)
>> file.info("foo")$size
>[1] 1e+05
>
>Cheers,
>Simon
>
>
>> Thanks!
>>
>> --j
>>
>> --
>> Jonathan A. Greenberg, PhD
>> Assistant Professor
>> Department of Geography and Geographic Information Science
>> University of Illinois at Urbana-Champaign
>> 607 South Mathews Avenue, MC 150
>> Urbana, IL 61801
>> Phone: 415-763-5476
>> AIM: jgrn307, MSN: jgrn...@hotmail.com, Gchat: jgrn307, Skype:
>jgrn3007
>> http://www.geog.illinois.edu/people/JonathanGreenberg.html
>>
>> [[alternative HTML version deleted]]
>>
>> _______________________________________________
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>> r-sig-...@r-project.org
>> https://stat.ethz.ch/mailman/listinfo/r-sig-hpc
>>
>>
>
>______________________________________________
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