On Sat, 2005-11-12 at 15:46 -0600, David Masover wrote: > Ming Zhang wrote: > > On Fri, 2005-11-11 at 16:56 -0800, Peter van Hardenberg wrote: > > > >>On November 11, 2005 05:59 am, John Gilmore wrote: > >> > >>>Does anybody remember GoBack? It was a versioning > >>>system for windows 95/98 that was incredibly flexible and useful. Tracked > >>>all changes to the whole disk. Old versions of a file? no problem. grab an > >>>old version of a directory for referance temporarily? easy. Got a virus? > >>>revert the whole HD, and then grab the newer copies of your documents and > >>>saved games as needed. > >> > >>My thoughts on this: > >> > >>The versioning would be an audit plugin. When the file is modified, tag the > >>current version, copy it into a sub-directory (oh, I don't know, say > >>file/.revisions/<number/date>), and disable write access to it. You might > >>not > >>even need extended filesystem attributes for this, but they would be handy > >>for tagging particular versions. > > > > > > if a file is opened, modified 2 times, then closed. u will only generate > > 1 version right? so "When the file is modified" is inaccurate. > > How about "When the transaction was completed?" Why does it matter?
then how u define a transaction? i mean we first need to choose a good event/period to define what is a good meaningful version. > > >>Copy-on-write would make this action extremely cheap, only adding a couple > >>of > >>extra writes to make it work. > > > > > > add 1 line at the beginning of a 100MB text file will make this uncheap. > > Who has to work with 100 meg text files? And why has this person not > broken them down into 100 kilobyte text files? Storage efficiency isn't > really an issue there... yes, 100MB/s text file is an extreme example, but a common case can be u delete 1 frame in a streaming media file. basically, a cow is not good for a data shift situation. u have >99% data unchanged, just their offset in file is changed. this lead to all blocks changed, then COW will need to copy a lot. > > Anyway, I think the main win is from copy-on-write for the whole file. >
