| Re: maximum LUN [message #64005 is a reply to message #63928] |
Tue, 25 November 2008 00:34   |
R.Bauer
Messages: 1424
Registered: November 1998
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Senior Member |
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Jeremy Bailin schrieb:
> On Nov 24, 1:30 pm, Reimar Bauer <R.Ba...@fz-juelich.de> wrote:
>> greg.a...@googlemail.com schrieb:
>>
>>
>>
>>>> What reason could there possibly be for having hundreds
>>>> of files open simultaneously? The only thing that comes
>>>> immediately to mind for me is a poor programming concept. :-)
>>> I kind of expected that reply... :) I think I do have a valid
>>> application, though. I have an archive of a few thousand satellite
>>> images, each of which has 6 bands, stored in separate files. I've made
>>> an object which can handle the six bands and return a subset image for
>>> a selected region processed as I want it. It also returns the image's
>>> coverage of the region, so that I can fill in any gaps with data from
>>> other images. This I do by opening further image objects. So far, I
>>> can use four of these to make an on-the-fly mosaic before I run out of
>>> LUNs - and it works well up to that point. The program allows zooming
>>> and panning, so I need repeat access to similar regions of the same
>>> files. I think it would be too slow to close and reopen them every
>>> time, so the objects hold the files open. The archive is several
>>> terabytes, changing, and not in my control - so preprocessing is out.
>>> With 128 LUNs instead of 28 I could mosaic about 20 image subsets,
>>> which will be enough for the moment. Still, if the number 128 was just
>>> an arbitrary choice long ago, I'd like to ask early for a bigger one!
>>> cheers,
>>> Greg
>> close and open costs nothing. The code between both lines can be
>> efficient or not.
>>
>> cheers
>> Reimar
>
> Not exactly "nothing", but about 0.2 ms for me:
>
> IDL> s1=systime(/sec) & openr,1,'foo' & close,1 & s2=systime(/sec) &
> print, s2-s1
> 0.00021815300
> IDL> s3=systime(/sec) & s4=systime(/sec) & print, s4-s3
> 6.9141388e-06
>
> -Jeremy.
Now we can discuss about your computers clock ;)
cheers
Reimar
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