[darcs-devel] announcing darcs 2.0.0pre1, the first prerelease for darcs 2

David Roundy droundy at darcs.net
Mon Dec 17 15:18:59 UTC 2007

On Thu, Dec 13, 2007 at 07:19:02PM -0800, Stefan O'Rear wrote:
> On Thu, Dec 13, 2007 at 07:12:45PM -0800, David Roundy wrote:
> > Still on my todo list (of issues that you've reported):
> > 
> > 2. figuring out a nice way to speed up a lazy darcs get.  Currently it
> >    grabs each file in the repository individually.  This means we're not
> >    harmed by long history, but we suffer greatly in repositories having
> >    many small files.  Note that these grabs are cached (if you enable a
> >    cache) so a second get of the same (or a similar) repository would be
> >    lightning fast.  But something should be done to (perhaps optionally)
> >    speed up darcs gets.  Perhaps we could download a tarball of
> >    _darcs/pristine.hashed with which to seed the cache (or our own
> >    prisine.hashed).  We could do similarly with the patches directory, in
> >    fact.  And in neither case would an "old" tarball harm us in any way
> >    (except requiring that we grab a few more files).
> My (incomplete) understanding is that the majority of the cost consists
> of round trips (request -> responce, and TCP handshakes) - so just
> adding HTTP/1.1 pipelining support to Darcs should give almost all of
> the benefits of a tarball, without requiring a new repository format.
> (Darcs' non-use of pipelining is also a frequent point of snickering, if
> you care about such things).

Any suggestions how to go about doing this? I quick look suggests that
libcurl can't handle http pipelining, and that no haskell HTTP library does
so.  The only library I can find that does seem to support it is libwww,
which looks like a real pain to use.

On top of this is the question of how to execute downloads in parallel.  I
presume this would require writing some threading code and hints like par
to spark off parallel downloads.

Is anyone interested in taking this on? It's definitely way beyond the
scope of what I will have time for.
David Roundy
Department of Physics
Oregon State University
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