5
(I think this is pretty brilliant. :-)
7
Branches diverge when people create more than one changeset following
8
on from a common ancestor::
13
We also allow branches to reunite. This means that all the decisions
14
taken on multiple branches have been reconciled and unified into a
17
A: 0 ------- 1 ----- 3
21
The predecessor of 3 is 1, in the sense that it was created on that
22
branch. We could have created the exact same state as a successor to
23
2, and we can move that state onto branch 2 without any loss of
26
(One thing we can do here is just delete B. Because all of the work
27
there has been merged onto A, this will not lose anything. We might
28
do this if the purpose of B has been achieved, such as completing a
29
feature or bug. But if the work is still in progress, we might keep
30
it around. It makes little difference whether we decide to do new
31
work in a branch called B or make a new one called C.)
33
That is to say that 3 can be perfectly (trivially) merged onto B,
34
with, say ``bzr push``, ``bzr pull`` or ``bzr update`` (whatever name
35
works best). Perfectly merged means that we know there will be no
36
conflicts or need for manual intervention, and that we can just
37
directly store it without forming a roll-up changeset.
39
I think we might also like the choice of merging A onto B, rather than
40
pulling the changeset. That causes a new changeset to be created on
41
B, noted as a successor of 2 and 3::
43
A: 0 ------- 1 ----- 3 ------+
45
B: \------ 2 ----+---------- 4
47
One complication is that 3 is probably stored in A's history as a
48
patch relative to 1; we can't just move this representation across.
49
Instead, we need to recalculate the delta from 2 to 3 and store that.
51
Despite that the delta is stored differently, the original signature
52
on 3 should still be valid. So it must be a signature of the tree
55
Note from `Kernel Traffic discussion`__:
57
__ http://www.kerneltraffic.org/kernel-traffic/kt20030323_210.txt
59
But anyway, what made Bitkeeper suck less is the real DAG
60
structure. Neither arch (http://arch.fifthvision.net/bin/view)
61
nor subversion seem to have understood that and, as a result,
62
don't and won't provide the same level of semantics. Zero hope for
63
Linus to use them, ever. They're needed for any decently
64
distributed development process.
66
This in turn suggests that possibly deltas should be stored separately
67
from the commits that create them. Commits name points of
68
development; deltas describe how to get from one to the other.
70
The separation is nice in allowing us to send just a delta when
71
diffing trees or recording for undo. We might want to compute many
72
deltas between different trees.
74
Is this a problem? Does this ignore Tom's advice about the primacy of
77
Splitting them is probably good, but then what manifest is stored in
78
changesets? We don't want to store the manifest of the whole tree if
79
we can avoid it. So I suppose the changeset just gives the hash of
80
the manifest, and the manifest then can be stored separately, possibly
added
removed
doc/join-branches.txt
