On Thu, Jul 09, 2015 at 02:03:15PM +0900, Mike Hommey wrote: > On Mon, Jul 06, 2015 at 03:54:35PM -0700, Junio C Hamano wrote: > > Mike Hommey <mh@xxxxxxxxxxxx> writes: > > > > > One of the first things parse_from does is unconditionally throw away > > > the tree for the given branch, and then the "from" tree is loaded. So > > > when the "from" commit is the current head of the branch, that make > > > fast-import do more work than necessary. > > > > If it is very common that the next commit the input stream wants to > > create is often on top of the commit that was just created, and if > > it is very common that the input stream producer knows what the > > commit object name of the commit that was just created, then > > optimising for that case does not sound too bad. It really depends > > on two factors: > > > > - How likely is it that other people make the same mistake? > > Looks like the answer is: very. Assuming my quick glance at the code is > not mistaken, the same mistake is made in at least git-p4.py (yes, the > one that comes with git), felipec's git-remote-hg, and hg-fast-export, > and that's 100% of the sample I looked at. > > I won't claim to know what fast-import is doing, not having looked at > more than the parse_from* functions and the commit message for 4cabf858, > but it seems plausible this also skips making tree deltas for those > trees. It doesn't /seem/ to be the case. > > - How bad the damage to parse_from() would be if we wanted to > > optimize for this case? > > I /think/ it would look like this (untested), which doesn't seem too > damaging: It's actually not enough. It does avoid to reread trees, but it doesn't avoid the pack to be closed/reopened. Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html