Re: Mercurial vs Updated git HOWTO for kernel hackers
From: Kyle Moffett
Date: Tue Jun 28 2005 - 19:21:25 EST
On Jun 28, 2005, at 17:54:14, Horst von Brand wrote:
Andrew Thompson <andrewkt@xxxxxxxxxxx> wrote:
I believe this works because the files stored in a binary format that
appends new changesets onto the end. Thus, truncating the new stuff
from the end effectively removes the commit.
And is exactly the wrong way around. Even RCS stored the _last_
version and
differences to earlier ones (you'll normally want the last one (or
something near), and so occasionally having to reconstruct earlier
ones by
going back isn't a big deal; having to build up the current version by
starting from /dev/null and applying each and every patch that ever
touched
the file each time is expensive given enough history, besides that any
error in the file is guaranteed to destroy the current version, not
(hopefully) just making old versions unavailable). It also means that
losing old history (what you'll want to do once in a while, e.g.
forget
everything before 2.8) is simple: Chop off at the right point.
If we have versions A through A+N, Mercurial will create a new revlog
file and
store a new full version when the total size of the changes between A
and A+N
is greater than a certain amount, effectively ensuring that
retrieving the
latest version of a file is O(size-of-file) instead of O(size-of-
file*revisions).
This is the same speed as RCS for the tip, and significantly faster
than RCS
for non-tip, which is crucial for merges.
Cheers,
Kyle Moffett
--
There are two ways of constructing a software design. One way is to
make it so simple that there are obviously no deficiencies. And the
other way is to make it so complicated that there are no obvious
deficiencies.
-- C.A.R. Hoare
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