Rich Freeman on 25 Oct 2012 13:42:49 -0700

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Re: [PLUG] git-fu

On Thu, Oct 25, 2012 at 3:50 PM, Frank Szczerba <> wrote:
> On Oct 25, 2012, at 3:18 PM, Rich Freeman <> wrote:
>> git has a real beauty to it, though some things are surprisingly hard
>> to do compared to rcs/cvs.  With cvs it is very cheap to compare two
>> versions of a file, since it just stores the diffs per file.  With git
>> the only way to tell what the differences are between two commits is
>> to walk the entire tree doing comparisons (though this is greatly
>> aided by the fact that everything is hashed already).
> I'm not sure what you mean here. Are you talking about the work git has to do behind the scenes? From a user perspective it's simple:
> $ git diff refA..refB path1 path2 path3....
> This is very fast, even on a large repo like the kernel sources.

I was talking about behind the scenes - that git diff has to open
dozens of files doing line-by-line comparisons across them to identify
the affected blobs, and then do a full compare on the blobs
themselves.  rcs would just look at one file to do the same.

Of course, it is a bit of apples-and-oranges since cvs/rcs has no
concept of a commit in the first place, in the sense of a group of
files changed atomically.

The git tool does a really good job of hiding the complexity and is
very fast.  In practice diffing two git trees is very quick since they
are, after all, trees.

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