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Re: apr_file_copy performance on Win32

From: Peter N. Lundblad <peter_at_famlundblad.se>
Date: 2004-11-02 22:02:09 CET

On Tue, 2 Nov 2004, Will Dean wrote:

> "Peter N. Lundblad" <peter@famlundblad.se> wrote in message
> news:Pine.LNX.4.55.0411022054280.8648@fnapp.local...
> I don't think anthing 'stat' is particularly standard.
Well, standard in POSIX, which is an ISO standard:-) But let's stop there.

> I would say
> #define APR_COPY_BLOCK_SIZE 65536
> would be as good a way of dealing with this as any.

> > We have a special version of file copying already. Using our own loop
> > wouldn't be much code duplication. So, if this is a problem, we could do
> > this as a short-term solution.
> Are you saying that there's an equivalent copy function in SVN which is
> sometimes used instead of the APR version?
We have svn_io_copy_file, which calls apr_file_copy, but has some special
cases for permissions on Win32, since APR seems to be broken on that
platform. I'm proposing to just not use APR, but instead do our own copy

> There does actually need to be a little bit of thought into the block size -
> in my very limited benchmarking here, copying a 8Meg-ish file, you get the
> following results:
> 512byte blocks - about 2 seconds
> 4096byte blocks (the default using fwrite/fread) - about 1 second
> 102400byte blocks (that's SVN_STREAM_CHUNK_SIZE) - about 800-900ms.
> any power of two sized block from about 16384 upwards - about 350ms.
> Although tiny blocks are slow for obvious reasons, there is clearly some
> other pathology here for larger block sizes, probably an interaction with
> underlying file-system block sizes (clusters, etc)
Clusters and page sizes and whatever.

> However, I'd be suprised if 65536 turned to be a bad choice on any system,
> and I can't believe it would be worse than 512!
A large power of two should be good, as you suggest.

> > Ofcourse, getting it into APR is even
> > better. Have you asked the APR people?
> I haven't dared. Would a change like this make it into APR and through to
> SVN in any human time-scale?
NO idea at all. Still, that would benefit other APR users as well. There
is nothing wrong with letting them know.


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Received on Tue Nov 2 21:54:05 2004

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