On Sat, Jun 23, 2012 at 9:15 AM, Branko Čibej <br...@apache.org> wrote: > On 23.06.2012 00:23, Vincent Lefevre wrote: >> Thanks for the explanations. >> >> On 2012-06-22 00:18:50 +0200, Stefan Fuhrmann wrote: >>> xdelta uses fixed-size 100kByte deltification windows. >>> The Changelog file in question is >400k, i.e. 4+ windows. >>> You insert about 2k at the beginning of the file, moving >>> the older parts by a similar distance. At the beginning >>> of each delta window, those 2+k don't have deltification >>> partner. Expected delta size: > 4 x 2kBytes. >> Wouldn't it be possible to change this size of deltification windows, >> with a command-line option (for svnadmin dump) and/or an option in >> the config file? >> >> The gain would be quite important on some kinds of changes (typically >> ChangeLog update), and a dump of a revision is something that could >> be done once and for all, so that it would be worth to spend time on >> optimizing it. > > It's not that simple, unfortunately. Currently both the delta generator > and especially the delta combiner expect the windows to be a known, > constant size. You can't just change them without affecting a /lot/ of code. > > Frankly I don't know how to make all the delta code paths gracefully > deal with variable window sizes. I'm sure it can be done, but the ROI at > this point is not good at all.
It's a shame that we didn't include the window size in the encoding of xdelta windows back in the day. Oh, well, a lesson for the future, I suppose. -Hyrum -- uberSVN: Apache Subversion Made Easy http://www.uberSVN.com/
