[daip] AIPS question

[Eric Greisen]

Assaf Horesh wrote:
> HI , 
> 
> I recently installed AIPS on my macbook pro. 
> It works just fine but when working with EVLA data that consist of 16IFs (Large bandwidth, fits file of 50Gb) it is very slow. 
> I was wondering if there is some AIPS parameters that I can tweak in order to make it work faster. 
> For example I noticed that when I run the TVFLG on my data it takes about 30 minutes to load up and mainly what is working is the hard drive (its reading/writing at 50Mbs rate) while the memory that is used by AIPS at that time is about 2.1 MB. Is there a way to make AIPS to use more memory to speed it up? is there any other tweaking I can do? 

I am afraid there is little one can do.  Reading 50 Gbytes from a disk - 
esp ones in laptops that have to run slower because of heating issues -
just takes time.  You should watch your adverbs closely however - if you 
do a multi-spectral channel, multi-IF TVFLG all at once you have posed 
an immense problem.  Doing 1 IF, averaging spectral channels, using 
limited time ranges or sources (do only cal sources to start) and the 
like will speed things up.  It constructs a UV-data image file and works 
from that - you can't decease your data set but you can control the size 
of the image to some extent and TVFLG will work much faster internally 
on smaller images.  The issue is really not memory.  If the work file 
(the image) is small enough, the OS should keep it in dynamic IO memory 
and it will not go to disk much.  However, during the build phase the 50 
Gbyte file truely has to come from disk.

Perhaps the Mac OS has tuning parameters to encourage the OS the use 
more memory for disk cache.  LINUX under RedHat anyway uses a great deal 
of disk cache if there is memory available.

Eric Greisen