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20010809: IMGLIST vs IMGCOPY using NEXRAD data

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  • Subject: 20010809: IMGLIST vs IMGCOPY using NEXRAD data
  • Date: Tue, 14 Aug 2001 21:12:10 -0600
>From:  Rick Kohrs <address@hidden>
>Organization:  SSEC
>Keywords:  200108091622.f79GMP122796 McIDAS nexradir nexraget

Rick,

Sorry I couldn't get to this last week, but I was hosting a McIDAS training
workshop.

>I have been working on some composite radar images and have noticed that
>my IMGLISTs are running 2-3X longer than my IMGCOPY commands. Here is an
>example pair:
>
>IMGLIST NEXRAD/BREF1 FORM=EXP ID=MPX DEV=T RAD_PROD.DOC R  
>IMGCOPY NEXRAD/BREF1 RADCOMP/TEMP.1 SIZE=SAME STYPE=VISR ID=MPX        
>
>My thought was that both getserver and dirserver would use the same
>algorithm for searching/sorting and the getserver would have the extra
>task of passing the data down to the client.

They do.  They go through the exact same code.

>If this was the case, IMGCOPY should take longer to run.

If you always do the IMGCOPY after an IMGLIST, then the files in the
input dataset are cached by the OS.  A second IMGLIST right after the
first one should be as fast the IMGCOPY.  I just ran such a test to one
of our servers, and the results were as I expected.  If you did the
IMGCOPY first and the IMGLIST second, your results should be reversed.

>Any thoughts?

OS caching.  Let me know if you disagree with this conclusion.

Tom
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