Shawn O. Pearce wrote: > Liu Yubao <yubao.liu@xxxxxxxxx> wrote: >> In current implementation the loose objects are compressed: >> >> loose object = deflate(typename + <space> + size + '\0' + data) > ... >> * Question 1: >> >> Why not use the format below for loose object? >> loose object = typename + <space> + size + '\0' + deflate(data) > > Historical accident. We really should have used a format more > like what you are asking here, because it makes inflation easier. > The pack file format uses a header structure sort of like this, > for exactly that reason. IOW we did learn our mistakes and fix them. > > If you look up the new style loose object code you'll see that it > has a format like this (sort of), the header is actually the same > format that is used in the pack files, making it smaller than what > you propose but also easier to unpack as the code can be reused > with the pack reading code. > > Unfortunately the new style loose object was phased out; it never > really took off and it made the code much more complex. So it was > pulled in commit 726f852b0ed7e03e88c419a9996c3815911c9db1: > In fact the format I proposed in my patches is uncompressed loose object, not uncompressed loose object header, that's to say I proposed format 2 in my question 2, I am just curious why the loose object header is compressed in question 1. I did a test to add all files of git-1.6.1-rc1 with git-add, the time spent decreased by half. Other commands like git diff, git diff --cached, git diff HEAD~ HEAD should be faster now although the change may be not noticable for small and medium project. > Author: Nicolas Pitre <nico@xxxxxxx>: > > deprecate the new loose object header format > > > > Now that we encourage and actively preserve objects in a packed form > > more agressively than we did at the time the new loose object format and > > core.legacyheaders were introduced, that extra loose object format > > doesn't appear to be worth it anymore. > > > > Because the packing of loose objects has to go through the delta match > > loop anyway, and since most of them should end up being deltified in > > most cases, there is really little advantage to have this parallel loose > > object format as the CPU savings it might provide is rather lost in the > > noise in the end. > > > > This patch gets rid of core.legacyheaders, preserve the legacy format as > > the only writable loose object format and deprecate the other one to > > keep things simpler. > Thank you for dig it out for me! Best regards, Liu Yubao -- 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
