| Re: time cost for file reading increasing!!! same file! [message #69746 is a reply to message #69733] |
Mon, 08 February 2010 18:04   |
wlandsman
Messages: 743
Registered: June 2000
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Senior Member |
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On second thought, the OP is only reading, not writing, to disk, so
the memory cache may not be relevant.
On Feb 8, 9:00 pm, wlandsman <wlands...@gmail.com> wrote:
> On Feb 8, 6:20 pm, minchen <mchen...@gmail.com> wrote:
>
>> 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.
>
> I am reaching here, but maybe the problem is similar to one discussed
> in an earlier thread (http://tinyurl.com/yzrvd96) where the correct
> question should be "Why is the file reading so fast to start
> with?" Those fast times are deceptive because the IDL thinks the I/
> O operation is complete after it has passed the data to the memory
> cache, but the OS has not yet written the data to disk. Once the
> memory cache fills, then IDL has to wait until the data is written to
> the mechanical disk, but those longer times are a better measure of
> the time to write the data to disk.
>
> --Wayne
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