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time cost for file reading increasing!!! same file! [message #69753] Mon, 08 February 2010 15:20 Go to previous message
minchen is currently offline  minchen
Messages: 8
Registered: February 2010
Junior Member
Hi everyone,
I meet a mysterious problem on IDL file reading.
The problem is as following:
I just read the same hdf5 file seveal times and see the time costing.
I find the first 270 file reading is very quickly but after that, the
reading speed drops down although the file is the same one.

The simple code is here:
pro try
filename='./particles.h5'
file_id=h5f_open(filename)
for i=1,2 do begin
i=1 ; here just for test, so it will
always read
print,'Systime=',Systime(0) ; here output the systime
dataset_name='Electrons_at_PE_302'
dataset_id=h5d_open(file_id,dataset_name)
ptcl0=h5d_read(dataset_id)
h5d_close,dataset_id
endfor
h5f_close,file_id
end

I have check the memory, it does not increase. So the memory should no
problem.
Why the reading time increase? I am also sure there is no problem with
the hard disk heating.
So, what's the problem?
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