comp.lang.idl-pvwave archive: archive » point

Home » Public Forums » archive » point_lun is slow

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: point_lun is slow [message #17618 is a reply to message #17437]

Mon, 01 November 1999 00:00

George McCabe
Messages: 23
Registered: June 1997

Junior Member

hello and thanks for the reply Liam,

i reason that the record size has to be larger than the seperation
between consecutive extracted elements in order for there to be a gain
in performance. the number of reads is reduced. also reading
sequentially in a chunk is faster than seeking to each datum, an
additional gain.

let's say the ratio of data read to data extracted is 'R'.

(the time it takes to seek and read the extracted data only) divided by
(the time it takes to read sequentially and extract data) is 1 when R
is what value? my guess is 100. what are your thoughts?

george

In article <38187A7E.8E60823A@ssec.wisc.edu>,
Liam Gumley <Liam.Gumley@ssec.wisc.edu> wrote:
> The following pseudo-algorithm reads records (chunks) of data from the
> disk in sequential order. Only records that cover the specified read
> locations are actually read from disk. Each record is only read once.
>
> Sort the array of read locations from lowest to highest
> Set the record size to 512 bytes (you can experiment with record sizes)
> Set the old record number to -1
> Start a loop over the read locations
> For this read location, compute the record number in the file
> If the record number is different than the old record number
> Read the current record
> Set the old record number to the current record number
> End If
> For this read location, compute the byte offset within the record
> Extract data from the record at the byte offset
> End Loop
>
> This method should be just as efficient for small or large numbers of
> read locations.
>
> Cheers,
> Liam.
>
> --
> Liam E. Gumley
> Space Science and Engineering Center, UW-Madison
> http://cimss.ssec.wisc.edu/~gumley

Sent via Deja.com http://www.deja.com/
Before you buy.

Report message to a moderator

[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

Previous Topic:	Is there a way to keep axis text from scaling?
Next Topic:	IDL 5.2.1 -- bug in filled contours?

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Wed Oct 08 19:29:19 PDT 2025

Total time taken to generate the page: 0.00457 seconds