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Re: point_lun is slow [message #17559 is a reply to message #17437]

Fri, 29 October 1999 00:00

korpela
Messages: 59
Registered: September 1993

Member

In article <381860B1.7145@gsfc.nasa.gov>,
George McCabe <george.mccabe@gsfc.nasa.gov> wrote:
> Struan Gray wrote:
>
>> simplest way to access this data be to use ASSOC to associate a huge
>> array of 2-byte variables with the file and then subscript it as
>> necessary to read in either frames or groups of individual pixels.
>
>
> Struan,
>
> ASSOC - certainly the simplest and also the fastest in cases where every
> element of the data is needed. but when for example only the
> [1538,395778,790018,... 434454018] location elements are needed from the
> file it is faster to point_lun to each. furthermore, the size of each
> associated read can affect the overall speed of a procedure. it's a
> better understanding of this subtlety that i am hoping for.

In this case memory mapping is definitely the way to go. Only accessed
pages get actually get read.

Eric

--
Eric Korpela | An object at rest can never be
korpela@ssl.berkeley.edu | stopped.
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[Message index]

		point_lun is slow By: George McCabe on Wed, 27 October 1999 00:00
		Re: point_lun is slow By: korpela on Fri, 29 October 1999 00:00
		Re: point_lun is slow By: korpela on Fri, 29 October 1999 00:00
		Re: point_lun is slow By: Liam Gumley on Thu, 28 October 1999 00:00
		Re: point_lun is slow By: George McCabe on Thu, 28 October 1999 00:00
		Re: point_lun is slow By: Struan Gray on Thu, 28 October 1999 00:00
		Re: point_lun is slow By: <karri on Thu, 28 October 1999 00:00
		Re: point_lun is slow By: George McCabe on Mon, 01 November 1999 00:00

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