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Re: Writing a very large file [message #57418 is a reply to message #57414]

Fri, 07 December 2007 12:39

pgrigis
Messages: 436
Registered: September 2007

Senior Member

Hi Wayne, I don't see this effect on my Mac...

Ciao,
Paolo

0 0.47319698
1 0.86947393
2 1.3010280
3 0.88083601
4 0.90536904
5 0.87050986
6 1.1563799
7 1.3074460
8 0.86915302
9 0.90732503
10 0.87124896
11 1.3134921
12 0.87872696
13 0.88537407
14 1.2747021
15 0.88525605
16 0.87100291
17 0.89240909
18 1.3015611
19 0.89991498
20 0.88492012

wlandsman wrote:
> I am writing a sequence of images to a single very large file on my
> Linux system. I find that the processing dramatically slows down
> after the first few images. The simplified code looks like the
> following:
>
> pro test
> ; Display the time required to write a series of image to a single
> large file
> im = intarr(4096,4096)
> t = systime(1)
>
> close,1 & openw,1,'test.dat'
> for i=0,20 do begin
> writeu,1,im
> print,i,systime(1)-t & t = systime(1)
> endfor
>
> close,1
> return
>
>
> IDL> test
> 0 0.22054195
> 1 0.26708603
> 2 0.35127902
> 3 0.37285185
> 4 3.3877730
> 5 6.1666460
> 6 6.1697872
> 7 6.2481630
>
>
> So the first four images take ~0.3s each to write, while subsequent
> images require more than 6 seconds each. I suspect that the slowing
> down is due to IDL (or the OS) needing to extend the file size. (I
> checked that it is not a memory usage problem.) So I think
> things would speed up if I could specify the final file size at the
> beginning -- perhaps there is a way to do this in Unix? I have
> experimented with the BUFSIZE and RAWIO keywords to OPENW but so far
> without any improvement.
>
> Thanks for any suggestions, --Wayne

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[Message index]

		Re: Writing a very large file By: Bringfried Stecklum on Sat, 08 December 2007 08:19
		Re: Writing a very large file By: Kenneth Bowman on Fri, 07 December 2007 20:50
		Re: Writing a very large file By: Jim Pendleton, ITT Vi on Fri, 07 December 2007 13:47
		Re: Writing a very large file By: Jean H. on Fri, 07 December 2007 13:23
		Re: Writing a very large file By: pgrigis on Fri, 07 December 2007 12:39
		Re: Writing a very large file By: David Fanning on Fri, 07 December 2007 12:23
		Re: Writing a very large file By: wlandsman on Mon, 10 December 2007 07:24
		Re: Writing a very large file By: Kenneth Bowman on Mon, 10 December 2007 07:43

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