Sparse file performance (Was: Re: Sparse file criteria malfunction - binutils produces sparse .exe & .dll files)

[Rolf Campbell]

Christopher Faylor wrote:
>>I remade the executables in an old version of inetutils.
>>The numbers below show that only the larger ones are sparse
>>(so the relative overhead is small) and that stripping them
>>removes sparseness. 
> 
> 
> This is exactly the kind of data I was looking for.  It seems to me that
> this suggests that there really is no issue that we have to worry about
> in this case.
> 
> Out of curiousity, does building the executable 1) without debugging options,
> and 2) with the -s option, also result in non-sparse files?
> 
> I'll test this myself when I get back to a windows computer but that won't
> be for some time.
> 
> I really appreciate your checking into this, Pierre.
> 
> cgf
I did some profiling of sparse-files vs. non-sparse files.  I found that 
accessing sparse files is between 5% and 10% slower (on 1.3.22/Win2000).

I created a 3Meg, 6Meg, 10Meg and 40Meg file using cp /dev/zero.  I then 
copied each file using windows explorer (and then verified that the 
sparse bit was gone).

Then I ran 'time cat filename > /dev/null'  (i ran it a few times to 
make sure the file was cached).  The performance difference was:

40Meg: 5%
10Meg: 7%
6Meg: 10%
3Meg:  5%

This wasn't the most sofisticated test ever, I did not ensure that the 
files were equally fragmented on disk.  But, it does show that sparse 
files are notably slower.



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